ETM Contactless TPS Refit -- Details and Resources

January 28, 2016

I thought I’d share my Sacer contactless TPS refit experience. While there’s tons and tons of information online, there’s no single good and complete source, and there are a lot of details missing.

My daughter’s college car is a 2000 S70 GLT-SE, 115,000 miles. Symptoms included an ETS light that had been flickering for a while before it went solid, a Check Engine light, slightly rough idle, and terrible off-idle performance with the car limited to rough acceleration with lots of stumbling to only about 20 to 25 mph.

A code scan revealed a P0121 and a ‘bad signal’ code logged at the ECM, likely related to the bad TPS signal.

Quick googling revealed the likely culprit: a lingering, finally terminal failure of the ETM’s flexible plastic wiper strips on the primary and/or secondary TPS feedback pots.

Looking into the engine compartment, I saw an original white label ETM.

Since the car was throwing only the P0121 code with respect to the ETM, I immediately ordered the Sacer contactless SA300 TPS unit through Amazon and BestPixelRepair. To thwart Murphy – regardless of how badly he hates being thwarted – I also purchased a used late build date replacement yellow label part number 8644347 ETM out of another 2000 Volvo S70 GLT SE, thinking that if the contactless install went badly I could install the scrap yard unit and have it adapted and flashed at the local dealer.

ETM REMOVAL

I found a number of comments in various threads on various forums that say that the non-turbo removal is easy, but that the turbo removal is much, much more difficult. Some people removed their intake manifolds. Some accessed the ETM from under the car, presumably with the assistance of spider monkeys. However, I found an excellent removal video posted by XeMODeX on Youtube that showed the process for a turbo car in about eight minutes by removing the electric cooling fan assembly:

https://www.youtube.com/watch?v=Mx2BXvZpMtI

Now, the video is lightly edited, but it’s not shortened that much. Once having seen the video, it took me about thirty minutes to get down to the ETM and pull the last four bolts, and that’s taking my careful time and making sure I didn’t break any of the fragile plastic connectors or lose any of the bolts and screws.

ONE PROVISO: the video shows the tech lightly pushing the upper intercooler tube attached to the ETM under the intake lightly out of the way while he lifts the fan assembly out. That was simply not going to happen with mine. The upper intercooler tube is rigid. It does bend, but not easily. It took me leaning on it, hard, to push it far enough back to clear the fan assembly. And of course at that point I have no hands left to lift the fan out. What I did was use Universal Tool #2, a coat hanger, and Universal Tool #3, vise grips, as a giant twist tie to hold the upper I/C tube back to a convenient intake manifold boss. Push, twist, push, twist, etc., until it’s back far enough to clear the fan when it lifts out. I was afraid I was going to break it, but the plastic is tough and bent back that far without a single pop or creak.

ANOTHER PROVISO: you may see comments from some folks who say that even in the event that their ETM had already been replaced under the extended warranty with a yellow label unit, the ETM pigtail might be routed under the inside starter bracket. Mine, being even more original and a ’00 instead of a ’99, was. It’s no big deal. Pull the two small nuts on the back of the starter’s studs and the one large bolt holding the bracket to the block, and the pigtail slides right out. In fact, you don’t even have to remove the two nuts. Just loosen them. Since the studs will be badly rusted, the nuts won’t turn easily and loosening them leaves them on the studs to mitigate their unavoidable loss if removed.

ETM TESTING

There are a large number of comments online that the Sacer refit should only be attempted in the event you see P0121 or P0221 codes only. These codes mean that the ECM is communicating with the ETM, but that the signal coming from the pots is logged bad by the ETM itself. This means the ETM is running its software load correctly – or at least thinks it is – and is simply letting the ECM know that it’s got a problem with the pot signals. Fine.

But you should still test the ETM for three reasons: first, you’ll need the default butterfly position voltage to calibrate the contactless sensor and thus hopefully avoid a re-flash and re-adapt; second, because if you find, for example, that the pot supply voltages aren’t nominal 5VDC, it means that you’ve got an internal ETM power supply fault and not necessarily pot wiper failures; and third, if the unit isn’t even initializing, it will mean you’ve got a drive failure and the unit can’t initialize itself properly on start-up, and might just be interpreting that as a bad signal. I suspect the latter condition is likely to cause more codes… but I’ve seen stranger things.

HERE WE HIT A PROVISO AGAIN, one of those little details that isn’t discussed anywhere: the instructions online and in the BestPixelRepair literature will tell you to pull the ETM but leave it connected to its 6-way harness interface down on the K-frame’s crossmember. You can park it up on the radiator bulkhead and the pigtail still reaches its connector. However, if you followed a tutorial like the XeMODeX Youtube video, you will have disconnected two harness junctions required to get power to the ETM. Near both the upper right and upper left corners of the radiator there are pairs of six-way connectors. When I tried to power up the ETM, I got, at best, misleading signals. A search at the link below revealed my wiring diagrams, and they showed me some 6-way connectors between power and ETM that needed to be plugged in. They looked suspiciously like the 6-ways I’d disconnected to pull the radiator:

http://www.volvowiringdiagrams.com/volvo/V70XC%20Wiring%20Diagrams/TP3943202%202000%20C70%20S70%20V70%20Early%20Version%20Wiring%20Diagrams.pdf

So. Now we have power to the ETM. First order of business, check to see if the unit initializes. When you move the ignition key from Off to Position II, the ETM will energize and then close the butterfly for a few seconds, all the while making a quiet whining noise. Then the butterfly relaxes and goes to default “off” position again.

If the unit doesn’t do that, it’s not initializing. A new sensor won’t help you. If the ETM drive is working, it will try to close regardless of sensor function.

If the ETM is initializing, we can move on to tear-down and further tests.

OPENING THE ETM AND MORE TESTING

Now we hit the first missing detail. It’s not a big one, but it will be a brick wall for some folks. Sure, you could reasonably argue that someone who is going to try this isn’t going to be slowed down, but…

The BestPixelRepair instructions don’t mention how to remove the cover of the ETM. It’s just glued on with sealant. On mine, the sealant was thicker on one side, and I pried up one edge with a small screwdriver working through that thick bead of sealant. Work your way around the edge, prying as you go with two small screwdrivers. The cover is very, very soft. It will deform. The edges will crush. You will need to straighten it before reinstall, which is likewise not a big deal. Be very careful with the screwdriver around the pigtail root, where the cable enters the ETM body. I don’t know how close the circuits are to the cover, but you don’t want to risk shoving the screwdriver down into the connector and damaging them. There is no metal housing rim under the edge of the cover adjacent to the pigtail root.

Now most of the illustrations you’ll find online and in the instructions will only show the ETM with the cover off and with the potting compound already removed around the contacts. The potting compound is that grey or green goo that fills up the volumes at either end of the ETM around the contacts. The potting compound serves several functions, and that will be very important later, when we discuss putting everything back together. For now I’ll just summarize what the goo does:

1) Seals the ETM housing…

2) Protects the ETM sensor and motor contacts from corrosion…

3) Prevents the ETM sensor and motor contacts from vibrating.

Given that the potting compound in my ETM was pliable and resilient, I’d say Magneti Marelli used some really good stuff. ( A side note – while all the HDPE convolute harness sheathing in my engine compartment was crispy powdered toast, the ETM pigtail convolute is in fantastic shape, flexible and free of cracks. It’s premium quality. This is really encouraging. While there are some forums that will complain bitterly about the ETM quality, the manufacturer certainly didn’t skimp on support materials. Furthermore, the fact that there is both a primary and a backup TPS tells us that the manufacturer knew the pots were compromises, and took steps to mitigate that – more signs of a conscientious design effort.)

Virtually all of the photos you’ll find of the ETM, already open, already with the potting compound scraped at least partly out, are dead-on from the direction of the cover. That’s not very helpful when you’re told to “scrape out the insulation” and you don’t know what’s under the “insulation” – the potting compound.

Here’s what a single contact looks like, and here’s another diagram that shows you how they fit within the ETM volume under the cover and under the potting compound:

The “3 contact end” has contacts that go to one of the TPS units only. The “5 contact end” has three contacts that run to the other sensor and two contacts that run to the direct drive butterfly motor. The cavities under the contact arrays pass through to the volumes underneath the caps of the sensors mounted to the ends of the ETM body. The sensor bodies have an o-ring around the round part that fits into the end of the ETM, but there is no seal around the rectangular projection that runs up the end in the direction of the ETM main cover. Thus, the potting compound forms an environmental seal between the engine compartment and the ETM interior.

How to best remove some of the potting compound? I fell back upon Universal Tool #1 – again, the small screwdriver. Here is where you’ll need to remove potting compound:

As shown, uncover the entire vertical tab portion of the contact, both sides, for those contacts circled in YELLOW, but you only need to expose the tips of those two contacts circled in BLUE. The two outboard contacts on the 5-contact side you needn’t touch at all; they can stay fully potted.

There are some nifty threads out there that discuss benchtop testing of the unit while hooked up to a 12-volt source. Well, that might be fine if you use a 12-volt battery, but I would be hesitant to use an actual 12 vdc power supply. Why? Because batteries run at something significantly above 12 volts, of course. An automotive electrical system runs between 13 and 14 volts, typically. The ETM contains an internal supply that runs supply voltage down to 5 vdc nominal. As finicky as these units are supposed to be, I could imagine that testing at 12 volts actual instead of 12 volts nominal would give you a bad calibration reading – given that some online sources claim that a variation as small as 0.2 v will mean you need a re-adapt.

Moreover, I know for certain that the ETM doesn’t contain particularly advanced or intelligent internal power management. Remember my comments above about hooking up the harnesses that were across the radiator before testing the ETM? Well, the first time I tried to test the ETM I had those disconnected, and I got some very unusual readings from the ETM pots. Specifically, I got a default butterfly position feedback value from both pots of a few hundred millivolts, and values at butterfly closed near zero, and at fully open of a few hundred more. The proportions were right, but the values were way too low. For a short while, before I realized I’d disconnected ETM power, I believed the internal 5 volt supply had blown, since the supply voltage was reading a little less than half a volt.

Remember this is with the main power – pin 6 of the pigtail 6-way connector – not receiving system power. However, the four connections to the ECM are still transferring signal and some power from the ECM to the ETM. It was trying to develop useful feedback voltages, but in the absence of chassis power it couldn’t, and I was just seeing bleed from the comm lines to the ETM sensor circuitry. This means that the sensor supply circuits aren’t completely isolated and aren’t completely regulated. If they were, I’d expect them to all be at zero volts with chassis power disconnected, even if the ETM is getting signals from the ECM. Thus… I will assume that slight increases in main power will be reflected by slight increases in signal power.

So what do we test next?

Those same threads that discuss bench testing show you where to test for potentiometer power and signal. But they’re not complete in presenting that information, and neither is the BestPixelRepair documentation, that simply says “check the voltage between the first and third pins.”

Now, if you were an engineer – and I am – and if you had experience building engine management components for production – and I do – then you might reasonably assume that the two sensors on either end of the ETM are identical. That is, that they are wired the same way internally and driven and read at the same pins, so that the signals on the pins leading to one sensor would be swapped with respect to the other, given that one sensor is rotated 180 degrees with respect to the second.

And you’d be wrong!

In fact, the two sensors are wired opposite to one another, so that the voltages on the three sensor pins are presented in the same order under the ETM cover. Here is a diagram that shows you what the signals are:

Of course if you only look at the magnitude of the signal voltage you’ll always be fine, and if you use a chassis ground when checking the 5 v supply you’ll be fine, too. But clarity and complete information is always better.

Now you can test them. With the ETM hooked up to the car and the ignition key in Position II – and good battery voltage -- you should see:

GND – 0 volts

Vss – 5 volts

Voutput @ default throttle position – 1.35 volts

Voutput @ closed throttle position – 0.6 volts

Voutput @ full open throttle – 4.4 volts

You should see these voltages at both ends of the ETM. When you move the butterfly through its range of motion, you should see smooth and contiguous variation between the limits of the range. And that of course is the whole issue with the plastic pots, as I saw:

3-contact side

Vss – 5.05 volts

Voutput @ default throttle position – 3 volts, very jittery from 0 to 4.

Voutput @ closed throttle position – 0.56 volts

Voutput @ full open throttle – 4.77 volts

Butterfly motion caused frequent dropouts to an unmeasureable voltage.

5-contact side

Vss – 5.05 volts

Voutput @ default throttle position –1.378 volts

Voutput @ closed throttle position – 0.587 volts

Voutput @ full open throttle – 4.79 volts

Butterfly motion caused frequent dropouts to an unmeasureable voltage, the most notable being a consistent dropout over an extended range of butterfly positions at about one-third throttle.

And there you have your verification – good 5 volts inside the ETM, but bad TPS feedback from both the primary and backup units. It is time to replace the sensors.

CUTTING THE SENSOR LEADS

Again, details are lacking. The most detailed post I found said “remove a half a millimeter or so” of the sensor leads to disconnect them from the ETM contacts. More than one post suggested de-soldering them, but noted that they’re “difficult to de-solder.” Which is an understatement, because they’re not just soldered; they’re riveted as well! A tiny rivet protrudes from the sensor lead through a hole in the ETM lead, and then the joint is soldered as well.

Use a Dremel, with a HSS cutting bit, not a stone grinding bit. A cutting bit will generate almost no heat removing the soft copper, whereas a grinding bit will generate tons that will transmit right back into the board for the tens of seconds it takes to remove the material. I found using a 1/8” HSS cylindrical cutting/milling bit like this worked just fine:

The goal is to remove the sensor lead from the ETM lead and then push it away at the base of the ETM lead, like this:

Do this for all three contacts on the 3-contact end, and ONLY for the lead noted as Voutput on the 5-contact end. When the contacts are severed, remove the stock TPS sensor on the 3-contact side by removing the four bolts. Note that you’ve now violated the environmental seals between the engine compartment and the ETM interior volume on both ends of the ETM.

MORE DETAILS

You’ll need to cut off the extra length of the throttle butterfly shaft on the 3-contact end. The BestPixelRepair instructions say to remove as much as possible, but “not to go crazy”. That’s not particularly precise, and I suspect it’s the reason some people find they need to enlarge their magnet’s D-shaped hole. There’s a simpler rule. On mine, I removed everything that wasn’t threaded, knowing that the unthreaded portion of the shaft was irrelevant to the use of the mounting nut even if the threaded portion of the shaft isn’t long enough to reach through the nut all the way once the magnet is installed.

ADJUSTING THE VOLTAGE OUTPUT

Everyone agrees: adjusting the voltage is tedious and will take some time. They’re right. It is tedious. However, a little finesse will minimize the time you spend on it. There’s a D-shaped hole in the Sacer magnet that fits over the D-shaped shaft. Then you re-install the butterfly shaft nut to hold the fragile magnet down.

The D-shaped hole in the magnet gives you a couple degrees of adjustment, and unfortunately it allows the magnet to slop around on the shaft as well. However, there’s a part of the plastic ETM butterfly spring cover that has a diameter almost the same as the magnet diameter. You can use this to maximize concentricity as you adjust the magnet.

I’m not sure what the instructions mean by “full clockwise” or “full counterclockwise” to adjust voltage. And I don’t think it’s wise to use “clamps” to hold the Sacer TPS in place during adjustment. The plastic housing warps as it squeezes into its socket. I’m going to bet that will induce voltage changes, too. I screwed the sensor into place each time, but did not fully tighten the four screws. Retightening screws into an aluminum housing without inserts is a bad idea.

The first time I installed the magnet I made match marks on the magnet and butterfly spring cover with a very new Sharpie with the butterfly in the default position. I also locked the magnet down rotated as CCW as the D-shape hole would allow. So I had something like this:

I hooked up the ETM, waited for it to initialize, and took a voltage reading from the 3-contact side’s Voutput pin, and I saw about 1.65 volts. Clearly too high.

A NOTE ON BENDING THE SACER TPS LEADS

Most threads and instructions will note that it’s neither necessary nor desirable to solder the Sacer’s leads into place each time you install it during testing. That’s correct. It would be a nightmare of soldering and de-soldering, and you’d probably wind up overheating the ETM leads.

If you’ve cut down the old sensor leads as shown above and left the ETM contacts intact, then you can get great temporary connections by gently bending the ETM contact vertical tabs outward towards the TPS, and possibly by also bending the TPS leads SLIGHTLY downward towards the body of the ETM. Yes, they might loosen up after one or two installs and reinstalls, but if you’re careful and don’t bend anything much, even half a dozen cycles won’t fatigue any contacts anywhere near the point of cracking.

MORE ADJUSTING

Remove the Sacer TPS. Loosen the throttle butterfly shaft nut and magnet, and rotate the magnet in the direction opposite to the previous rotation with respect to the shaft, and lock it down. Make another match mark. You should see something like this:

Reinstall the Sacer TPS, hook up the ETM, and take another default butterfly position reading from Voutput on the 3-contact end – the value coming from the Sacer sensor.

I got about 1.1 volts.

I know I’m after 1.378 volts, and I can get from 1.1 to 1.6 with the adjustment available. That’s just more good news. There would be no cutting of the D-shaped magnet hole today.

After two more tries – disassembly, move magnet, reassembly, hookup, test voltage – I was here:

… and I was reading 1.367 volts. That’s a difference from the original unit of a hundredth of a volt and and change. Should be plenty close enough.

You don’t have any way of adjusting the sensor’s excursion, but I checked it anyway. At full throttle open my voltage was 4.69 and at throttle closed it was .55. Again, that should be plenty close enough. The ETM obviously initializes every time it starts, and hopefully those values would be close enough to the original sensor values that a re-adapt wouldn’t be required.

REASSEMBLY

I removed the sensor body one more time and tightened the shaft nut a bit, making certain I didn’t move the magnet on the shaft any. I applied some service removable penetrating threadlocker as a hedge against vibration inside the open end of the nut. Then I made sure the circular pocket into which the sensor body fits was nice and clean, as was the Sacer unit itself and its o-ring.

Because the previous sensor contacts were both soldered and riveted, you will need to tin the leads to get a good solder joint. I used a Weller WD1 station set to 720 deg F and Kester rosin core .040 Sn63Pb37 #50/245, which is a good all-purpose electrical and electronic solder. I scrubbed the four contacts I’d exposed completely with stainless steel wool and tinned them in about half a second each on their outside surfaces, where’d they mate with the Sacer leads or with the jumper wire. The fresh new copper leads of the sensor tinned even more easily, on the sides away from the main housing.

I applied a thin bead of high temperature RTV all the way around the edges of the rectangular projection over the Sacer’s leads, into and along the o-ring on the inside edge, gently gave the three leads a last slight downward bend, and re-installed the Sacer TPS. I tightened the screws this time.

At this point the tinned leads of the TPS will be abutted to the tinned leads of the ETM. It’s a good time to check voltages again to make sure nothing has changed. Nothing had: 1.367 volts at default throttle position. I touched the soldering iron to the junctions and the pre-tinned leads flowed together perfectly. I ran the secondary output wire along the inside edge of the ETM housing to the 5-contact end’s Voutput contact, trimmed, stripped, and tinned the wire, touched it to the tinned contact, and applied the soldering iron for a fraction of a second. It’s also a good idea to pot the jumper wire in place at several locations along its length so that it doesn’t vibrate loose; I used some dabs of RTV at half a dozen spots so that the wire is completely locked down.

Check the voltages again, at both sensor Voutput contacts. It should be the same at both and the same as what you had before. If not…. there’s probably the remains of a connection between the second sensor’s Voutput lead and the ETM contact to which is connected the wire from the other end’s new sensor.

DETAILS, DETAILS

At this point you could button it up and reinstall it. But there’s a problem.

It will fail.

Oh, it won’t fail right away, but it will sooner or later. While the new bead of RTV around the rectangular projection over the Sacer’s leads restores the environmental seal between the environment and the ETM interior on the 3-contact end, you’ve still got a breach on the 5-contact end, where the old sensor Voutput lead was pushed out of the way after being cut off. It’s a small breach, but a breach nevertheless.

But there are bigger issues.

Even if you’ve got perfect solder connections, they will eventually fail because they’re at the ends of tuning forks. All of those little copper and brass tabs sticking up, cantilevered, oh, they love to vibrate. This is why the old leads were both riveted and potted on top of being soldered. The solder is completely inadequate to preserve reliability by itself.

Some good 5-minute epoxy should take care of the seal at the 5-contact end and should mitigate the effects of vibration. Here’s some trivia: epoxy can be conductive, just like some silicone RTVs. Silicone isn’t a good choice for potting the contacts because it’s too soft and because there’s a good chance your RTV, especially grey or black varieties, is at least partially conductive. Likewise grey epoxy might be a little conductive. For potting electrical contacts, I prefer to use a clear 3- to 5-minute epoxy like the Gorilla Glue brand Walmart sells in double plastic syringes. Clear epoxies – especially consumer products – are rarely conductive at all because making them conductive would be both pricey and pointless.

I mixed up a teaspoonful and applied it with a tongue depressor in drips into the 5-contact end’s contact volume, making sure first the old sensor lead was pushed completely away from the ETM contact. I applied enough to mostly fill what I’d gouged out to gain access to the contact, and then added more to cover the tips of the two contacts I’d cleaned off as well. This restores the environmental seal at the 5-contact end and mitigates vibration effects on the 5-contact end’s solder joints, and provides a secondary environmental seal over those contacts in the even the main ETM cover is violated.

Against the tiny chance some epoxy would flow through the hole enlarged by disconnecting the old sensor’s lead, I kept moving the butterfly until the resin got sticky, at which point I knew it would stop flowing more deeply into the old sensor remaining on the 5-contact end.

I propped the ETM up on an angle so that the 3-contact end was higher than the 5-contact end. I dripped epoxy around the three contacts to the new TPS. I watched the epoxy flow around the contacts but prevented it from dripping under the Sacer cover, since I feared epoxy moving into the air gap between the sensor body and the magnet. Because I sealed the Sacer sensor body completely against the ETM housing, there is no longer a need to seal the ETM interior volume where the contacts pass through to the Sacer leads. Once the epoxy got a little sticky, I packed more into place to completely surround the new solder joints.

Guess what? It’s a good time to check the voltages again, after the epoxy sets. Did that. Butterfly moves cleanly and I get 1.367 volts at default position.

Clean out the ETM housing cover groove where the old sealant was – being careful not to gouge too deeply near the pigtail root – straighten out the cover with some pliers, and reinstall the cover with a bead of RTV in the groove.

Reinstall.

RESULTS

On start up, no ETS light, no Check Engine light, perfect idle, perfect off-idle acceleration. All fixed.

RESOURCES

Here’s all the useful links I found while researching the ETM issue.

http://www.volvowiringdiagrams.com/volvo/V70XC%20Wiring%20Diagrams/TP3943202%202000%20C70%20S70%20V70%20Early%20Version%20Wiring%20Diagrams.pdf

http://forums.swedespeed.com/showthread.php?174010-99-V70-GLT-no-acceleration-no-throttle-response

http://www.volvoxc.com/forums/showthread.php?21351-ETM-voltage/page3

http://www.volvoxc.com/forums/showthread.php?21351-ETM-voltage&s=40b6f7fcde245a5191ec46a4d7db400a

https://www.youtube.com/watch?v=Mx2BXvZpMtI

https://www.youtube.com/watch?v=KiR6HFvX8RM

http://volvospeed.com/vs_forum/topic/154005-etm-fix-idea/