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Magneti Marelli ETM testing and diagnosis help

Do you have a failing Electronic Throttle Module? What steps to take if you do, plus the latest ETM news. Volvo 1999-2002 models only please.
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Magneti Marelli ETM testing and diagnosis help

Post by prwood »

My '01 V70 2.4T has an ETM with the following label:
Magneti Marelli ETM with Yellow Label
Magneti Marelli ETM with Yellow Label
IMG_1209.JPG (70.84 KiB) Viewed 3300 times
I am currently experiencing an issue with the following symptoms (please note, these are all from idling in the driveway; I have not yet tried driving the car):

1. After starting the engine, RPMs drop to between 500-750, there is rough, loud stumbling sound coming from the engine, and there is a rhythmic puffing sound from the exhaust (approx. five puffs per second).
2. If I increase RPMs to 3000, it will stay at that point, but has a dip down to ~2800 RPM once every second or so.
3. When I release the accelerator, RPMs drop down immediately, and as soon as they go under 1000, the stumbling returns. Sometimes it returns and continues until I shut the car off, other times the engine immediately stalls.
4. If I push the accelerator all the way down while idling, the RPMs increase over 3000, but after a few seconds they drop and the engine stalls.
5. Using an OBDII scanner, the throttle position is reported as 20% immediately at startup and while idling, and continues to report as 20% regardless of how the accelerator pedal is pushed, even though the engine does seem to respond to action on the accelerator pedal.
6. Also on the OBDII scanner, MAF sensor reading is 0.6-0.7. MAF sensor was replaced in January of this year and was just cleaned this week.
7. The car *has* had the Volvo Recall 155 ETM software update installed.

I am planning to remove the ETM from the car tonight in order to clean and inspect it. I have a few questions:

a. If I remove the ETM from the intake manifold, but leave it connected to the wiring harness, are there any functionality tests I can carry out?
b. Are there any tests I can run on the ETM using a basic multimeter? Other than the OBDII scanner, this is the only other diagnostic tool I have access to.
c. If I disconnect the ETM from the wiring harness, can I connect it to a 12v power source to do any further tests? If so, which ports do I use to power it?
d. I plan to clean the bore and throttle plate with air intake/throttle body cleaner and a nylon brush. If I were to also remove the sensor panels from the sides, and the inspection panel from the front of the ETM, and spray out the insides with mass airflow sensor cleaner or quick-dry electronic connector cleaner, would this be helpful or harmful?

Thanks for any advice you can provide.
Cars I've owned:
- 2015 to current: 2001 Volvo V70 2.4T; 2004 Honda Odyssey
- 2007 to 2015: 2002 Subaru Legacy L Wagon
- 2003 to 2016: 2001 Toyota Corolla LE
- 1999 to 2003: 1994 Toyota Camry LE
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Joined: Sun May 10, 2020 2:11 pm
Year and Model: 1999 S70 T5
Location: Hungary

Re: Magneti Marelli ETM testing and diagnosis help

Post by beilagbela »

I know I'm super late, but I just came across your post and figured might post some info if anyone else comes across this.
Your symptoms sound like either one of the position sensors, or the control circuit itself inside the ETM has went bad, assuming all the wires are good. 20% throttle position is a mechanical failsafe and indicates that the ETM is unresponsive, it will stay at 20% throttle if the electric motor inside has no power (ignition off) or it's broken. The idea is that even if your ETM breaks, you should be able to drive to the nearest service center.
I'd try getting a helper and asking him/her to step on the accelerator pedal with the ETM plugged in but off the car so you can see what's happening. Important, your ETM will only function for 10 seconds after you turn the key for position 2, so if it's unresponsive after the initial 10 seconds with the engine not running, that's perfectly normal.
After those 10 seconds however (you'll know because the high pitch whine has stopped and the throttle plate "snapped" back to a default position) you can move the throttle plate by hand and the OBD scanner should record the changes in throttle position.

a) Kinda, the Marelli ETM does a self-test sequence when ignition is applied (it'll move back and forth a bit), and it will respond to the accelerator pedal inputs, however, only for 10 seconds after you switch the ignition on, after which it's going to "default" to 20-22% throttle position, not responding to any more pedal inputs until you either start it up ( DON'T try to start the car without the ETM in place) or you cycle the ignition again. Makes it hard or rather, impossible to diagnose the ETM with the engine off with a scan tool. :D

b) With the multimeter, there's two tests that the repair manual suggests: one is checking for supply voltage, that's done by disconnecting the ETM plug, and measuring the voltage with the ignition on between pin 6 and ground on the connector coming from the car (if you look at it from the front, the little notch on the connector that secures it into place facing upward, it's the pin on the bottom right) Typical value is 11-14V
The other test is checking for ground, the ETM is not grounded via connection to the engine like other parts, it has a dedicated ground wire. With the ignition off, check the bottom middle pin (pin 5 ) of the wiring harness on the car's side and ground. You should see close to 0 ohms. I disconnected the front cables when I removed the fan shroud, and that made my ETM not receive power, so make sure you connect the connectors running along the front of the car if you took the fan shroud off!

c) I wouldn't recommend it. The ETM is part of the CAN network and it needs to receive a signal from the ECU in order to move, so most likely nothing would happen if you tried, but you may end up damaging the ETM, i'm not sure. The car should supply power to the ETM on startup and conduct a self test every time, it has a characteristic high pitch "whine" when it's operating, followed by a springy, metallic sound of the throttle valve returning to 20% after 10 seconds on ignition.

d) You can clean the bore and throttle plate, it has helped many people, though I doubt it is the cause of the fault in your case.
Taking the side panels off is something I'd advise against unless you're planning a full rebuild. (Un)fortunately, everything is glued with silicone so there's a low chance of weather getting in, so cleaning it won't be necessary under normal circumstances, because all the contacts are "encased" in silicone, but if you try to remove either side panel, the soldered contacts of the throttle position sensor will break off and you'll have to resolder them.
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