After my daughter-in-law had the throttle cleaned and finally the ETM replaced on her 1999 V70 XC, for big dollars I decided to investigate. I ran a failure analysis lab for many years to this is right down my alley.

Make a note of what the ETM is. It is an electronic connection between your foot and the fuel injection system You can no longer open the hood and reach in to the throttle body (or carburetor on older car) and move the throttle manually. A failure of this part is like the linkage dropping off of the throttle body. It is a safety issue if it leaves you or you wife and kids stranded on the side of the road on a dark and stormy night.

What I have found from this site and others is:
The symptons are (any one or several):
Rough idle,
failure to start,
failure to proceed,
cleaning the throttle body sometimes helps,
might be heat related
my only be able to go 20 mph
Also, there is some talk that the maker of this module (Marelli) is no longer in business.
It will eventually fail on most if not all 1999, 2000 and 2001 70 series cars.

The fix: Eventually is to replace the ETM as a cost of up to $1000. It is not a DIY job as the software has to be reinstalled for your car. Used parts are not an option as they will fail also.

The extended warranty list does not include the ETM in "what is covered".
Volvo has not responded to replace this out of warranty and in some cases saw the problem and ignored it until the car was out of warranty.

Some postings said to contact the BBB, Ford and the NHTSA. I checked the NHTSA site under "Defect Investigations" and found only one entry on this problem. I would suggest that all Volvo owners that have had this problem call, write or got to the web site (www.nhtsa.gov) and file a complaint. It would be well to have a copy of your service ticket from the dealer and you VIN number when you call.

Hopefully, we can bring this "safety" issue to the forefront.

I would like two items resolved:
First: I want to know if the problem is fixed and we can feel confident that the car is safe for my daughter-in-law to use with the kids in it (this year one will be learning to drive.)
Second: We want to be reimbursed for the repair of this part.
Donald Willson

I beg to differ. I had no symptoms other than an idiot light that said "stop the car and restart" car was running fine. Went to dealer who pulled code as "ETM going soon". Without question, they replaced it under certified warranty and it cost me only a couple of hours and $50.

I have just received another failed ETM from an out of warranty car. I will have more informations in a few days.
Thanks for the information on removing the module.
I also looked at a new module today and externally it is from Marelli and looks the same. The Volvo part numbers are different though. Does any one have access to a Volvo parts book or microfiche?
Don

--
Retired Metallurgical Engineer and former manager of an electronics failure analysis laboratory for Rockwell International.

My car died during a rainy 5:30 commute rush home before the holiday weekend with my 2year old in the back seat. It was awful. I got it to my local garage (I quit using the dealer after they would not address my complaints of clunky acceleration and questioning of multiple O2 sensor replacements). The shop called to tell me that they cannot fix it due to a programming req. that is only available through the dealer. I now have an appt. with the dealer (soonest they can get it in is the middle of next week)at a cost of $1100.00+. I know what I'm getting for Christmas. Volvo for life, bummer.

Failure analysis of Marelli Electronic Throttle.

My previous post had on error. Marelli is not out of business, they are a large comglomerate that have many trademarks under their umbrella including Weber, Solex, Midas and others.

Summary:
The failure mode for the Volvo Electronic Throttle Module, made by Marelli and used on 1999, 2000 and 2001 70 series Volvos, is the wearing out of the thick film resistor on the two throttle butterfly position potentio-meters. It is not due to heat or due to a dirty throttle body. The time to failure is due to the accumulated movement of the throttle shaft, so in town stop and go driving with a lot of throttle shaft movement per mile will wear out the potentiometer film faster than a long distance driver with few throttle movements per mile.

First, let me introduce myself. As a Metallurgical Engineer I managed a failure analysis laboratory for Rockwell International for 20 plus years. I am very familiar with component failure analysis and have done or supervised thousands of analyses. In general, electronic components seldom fail; it is the mechanical parts in the assembly, such as, switches, potentiometers, variable capacitors, connectors and solder joints that fail. There is no need to be afraid of electronics, just the mechanical components.

Failure mode:
At the ends of the throttle module are black plastic caps. In the inside center of each is a ½ inch (approx.) bushing with a “D” shaped hole that fits over the end of the throttle shaft. Of course, this only turns less than ¼ turn, from closed to full open. Alastair, in a previous post, said there is a rheostat on each end. When I popped out a nickel sized spring retainer the bushing and rheostat were fully exposed. Alastair said he found the wiper, that was riding on a black resistor material, contacted with the ends of the wiper. On close examination I find that the wiper has two sets of four fingers riding on this resistance film. Again, as Alastair said, the wiper rides on the resistance film as if you were scratching your fingernail across a black board. They use redundant fingers so that if there is dirt on the film there will be several that are still making connection. My examination, at 10x magnification, found that the wiper is covered with the resistance film, enough to bridge the space between the fingers. On looking at the inside of the rheostat, the film it is grooved. Closer examination showed that the thick film resistance material was on a piece of flexible plastic film, like photo film, but probably Mylar. It looked like it could be pulled out so I tried. It came out and measures 7/16” x 2 5/8” with 2 strips of resistance material. The wiper has carved grooves deep enough that light shines through on the film (this was on the end that the external cord is clipped to.) At the other end is similar construction, though the resistance material has not yet been scraped away, though there are clear tracks and an accumulation resistance material at the end of the track, like you had raked a garden one way only. If I was a betting man, and since I have no way to do a full electrical test, I would place a big bet that this is the problem.

I consulted with a component engineer that worked with pots, switches, and other similar components. He verified my thoughts that there is no combination of materials for resistance film and wiper material and geometry that would work in this application. A metal wiper and a carbon film is the combination that is used on low cost radio volume controls, not a wiper that is going to see up to several thousand movements per mile. (Think – how many times does the engine power and thus the throttle position change per mile.) The only design for this throttle position sensor that would have live through 100,000,000 million movements per 100k miles (assuming a movement every 5 feet) must be some type of non-contact sensor.

Why two potentiometers? See http://www.auto-solve.com/etc.htm. This discusses the design of the throttle position sensors. There are two resistance signals from these potentiometers. The combined signal allows the ECM to calculate a mean voltage output from the two signals allowing the throttle butterfly position to be calculated with greater accuracy. Since it is critical to know the throttle position very accurately any degradation of the signals from the potentiometer would throw the ECM computer and its program into spasms.

Other components:
The circuit boards are made using DuPont ceramic thick film technology with gold, silver and silver-palladium interconnect. I found a good explanation of the materials of construction for this exact board at http://www.dupont.com/mcm/applic/H-78296.html. The advantage of the ceramic is low expansion with temperature extremes. The components are potted with a clear, elastic compound, probably a silicone (?). All components are visible. All connections from the boards to the outside connections are two aluminum wires that are welded to the board and appropriate feed-thru. Between the power board and the control circuit board are 11 connections that are single wires and 3 that are doubled, probably power and ground. All components, except resistors, are soldered down using surface mount technology, resistors are screened (painted) on and then trimmed to value by laser. Most passive components (resistors and capacitors) are connected by screened on traces. The active components (transistors, diodes and integrated circuits) are connected by welded wire bonds. Based on looking at thousands of circuit boards and thin film technology devices, I would rate these as excellent and very appropriate for the application.

The fix:
Replace the throttle module at the first sign of erratic running, rough idle, car can only go 20 mph in limp home mode. There has been a lot of talk about cleaning the throttle body of carbon and dust. Don't bother. Others said that the quality of gasoline or petrol made a difference, ain't so. Alastair and others opened these end caps and used circuit cleaner and achieved a temporary fix but the problem is still there, the resistance film is damaged and will continue to get worse.

Warranty:
There are several warranty out there. My son got one from Colorado First, a company under United Car Care. It specifically mentions what IS covered and the ETM is not mentioned. Volvo VIP warranty does cover it. I did find that the dealers cost on the module is about $338 and he marks it up to $535 plus labor plus software upgrade. Again, we all feel this is a safety issue, and a time bomb failure. It is not IF but WHEN.

Other comments:
Some had said that the replacement parts are Bosch. I called Bosch and the person I talked with said that was not so. I'll look at my son's car this afternoon and see if I can determine the manufacturer.

What we can do:
Call Volvo and register a complaint that this is a safety issue caused by a defective design. Tel: 1-800-458-1552
Email: customercare@volvocars.com

Call or email National Highway Traffic Safety Administration at (www.nhtsa.gov) or call 1-888-DASH-2-DOT.

Try to bargain with your dealer to give you the parts at cost.

I just checked the ETM installed on my son's 47,000 mile 1999 XC. It took a while to find the thing. It is on the front of the transverse engine, under the intake manifold and is an up flow device. Sounds reasonable since it is only air going through. To me it looks like you would have to remove the intake manifold which removes the ETM with it.

Without a positive verification it looks like the new ETM is just like the old one, a Marelli. So much for a positive fix.

Don Willson

The ETM can be removed without removing the intake manifold. remove the fan and shroud and there are 4 bolts that hold it to the manifold. Note the etm harness is routed between the block and a bracket for the starter andit must be remived or cut the harness to remove the plug. Another failure mode has been a hunting idle as a flat spot is worn on the shaft bushing

greasemonkeyjoe,

I have just finished opening up an out-of-warranty ETM. I find that the throttle shaft is supported by two very smooth turning sealed ball bearings. They show only slight carbon dust on the side facing the throttle bore. I have a hard time imagining any circumstance that would occur that would lead to a flat spot being worn on the shaft bushing.
On the thick film throttle position potentiometers the resistance film is work completely through to the backing film at an area that corresponds to the idle or slow speed throttle position. Since this tells the computer where the throttle is, the computer is getting erroneous information.
Unless he has hard evidence otherwise I think this might be another case of the mechanic trying to explain something that he is knows nothing about.

Don "Double L" Willson

I'm very interested in your posting which I highly appreciated.
I own a year 2000 S80 T5 which, despite the low mileage (just 45000 Km), is showing irregular idle, so I assume that the ETM "time bomb" issue is about to blow. The car is out of warranty.
I'd like to take advantage of your experience to understand why it is necessary to replace a $1000 ETM device when the faulty item is just a stupid potentiometer.
Wouldn't it be possible just to replace that potentiometer, thus avoiding the need to download the software and all the other stuff that comes along?
Are they telling us that we have to purchase the whole ETM because they can’t supply simply the broken part which is worth maybe 30$ ?
Or am I missing something ?
If you can confirm the part is Marelli branded and if you can provide some product code or exact description, I could try to enquire the manufacturer, since Marelli is an Italian brand and I happen to be Italian too.
Thanks in advance.
Andrew – Milano - Italy