ECC fault code --updated

95Volvo850 · Post by **95Volvo850** » 14 Mar 2010, 21:51

I checked the MOSFET with a DMMs (Fluke 77). It seems like it had enough voltage to turn the device on (source to gate) and then there was conductivity between source and drain. When putting my finger across the pins the MOSFET would turn off and then I had an open circuit between source and drain.

Do you think that that is not enough of a test? The fan doesn't run at all, so in case it is acting like and insulator. However, the code 4-1-8 says that there is "no control signal to blower fan power stage". That doesn't mean the power stage is faulty, right?

I cannot understand what "no control signal to blower fan power stage" means. What am I supposed to check? The Volvo manual has a procedure where you can measure voltage and conductivity between EEC and power stage, but you need a test box of some sort that I don't have.

Post by **Ozark Lee** » 15 Mar 2010, 18:28

I cannot understand what "no control signal to blower fan power stage" means.

Unfortunately that code is always vague - it just means that the system is mad about the power stage. Your test on the MOSFET sounds like a good test. If you have access to a function generator you could try applying a pulsating DC square wave to the input signal and see what happens. I am traveling at the moment and I don't have access to VADIS to give you an idea as to what voltage and frequency range you should use.

...Lee

95Volvo850 · Post by **95Volvo850** » 17 Mar 2010, 09:20

My main question here is: does code 4-1-8 necessarily imply a bad power stage?

After all it says "no control signal to blower fan power stage". Could that be caused by some sensor somewhere? I tried to locate the outside temperature sensor but I didn't find it and it seems to work anyway.

Post by **Ozark Lee** » 17 Mar 2010, 20:42

Normally the 4-1-8 code does mean a bad power stage but, from the guys who have torn the power stages down to component level that normally implies a bad MOSFET but your test on the fet sounded like a good test.

I think there is more to the power stage than the power MOSFET itself and it could be another component within the power stage that is bad. Sadly, no component level schematics are available from Volvo. The Official Volvo schematics show most of the electronic control systems as black boxes. I only have one car with ECC so I have left well enough alone as it seems to work fine and I have not gone after it with an oscilloscope or anything to reverse engineer it.

I am reticent to send you out to buy a new power stage since your MOSFET checked out ok and the Power Stage is not a cheap part. From previous posters that have similar problems it tends to run 70/30 between the power stage and the ECC controller but most of the folks with a bad controller have obvious damage inside of the controller itself after the case cover is removed and I believe you indicated that everything looked fine to the eye in the controller.

From your previous postings you know your way around circuits and electronic troubleshooting and I am stumped that you have seemingly good ends but not a good system. Have you ohmed out the wires between the ECC Controller and the Power Stage?

The only sensor on the power stage appears to be a feedback signal from the power stage.

We are not trying to give you the runaround but your problem is atypical.

...Lee

95Volvo850 · Post by **95Volvo850** » 18 Mar 2010, 10:49

I have checked the wiring between ECC and power stage and there is continuity. Is there a way to bypass the ECC controller and make the power stage turn on? I guess we would need the schematics for that...

BTW I found a blower power stage online for $20 (it's a replacement, not Volvo OEM). At a junkyard here in town they have it for $35 and the ECC controller for $50. So I guess I can try to get the power stage first and then take it from there...

The other alternative is to spend a few dollars and get a high power MOSFET and replace it anyway. You never know with semiconductors.

95Volvo850 · Post by **95Volvo850** » 22 Mar 2010, 13:44

Well, I performed additional in-depth wiring testing according to the Volvo manual. Voltage measurements indicated that "diagnostic signal from power stage" of 1V means no signal. So I felt a little more confident that the power stage was the cause of the problem.

I had a hi-power FET sitting around and I tried to replace the one in the power stage, but nothing happened. So I went to a junk yard and bought a used power stage for $35 and now everything seems to be working fine.

In short sentence, it seems like a 4-1-8 code does usually imply a bad power stage.

jbouzajr · Post by **jbouzajr** » 03 Apr 2010, 17:35

Hi guys,

I have this 4-1-8 code and it won't go away on my son's 93 850 GLT. I have been reading your posts on this subject and I have a question...What the Heck is a MOSFET?? Until now the only MOSFET I knew was a sound system....Thanks

Post by **Ozark Lee** » 05 Apr 2010, 18:06

What the Heck is a MOSFET?? Until now the only MOSFET I knew was a sound system.

Metal Oxide Semiconductor Field Effect Transistor. They do get used in power amplifiers often since they can handle a relatively large current flow.

...Lee

cpl · Post by **cpl** » 09 Jun 2014, 18:04

FCP Groton cabin temperature sensor OEM 9145736 $30.95 each

Post by **abscate** » 09 Jun 2014, 19:01

jbouzajr wrote:Hi guys,

I have this 4-1-8 code and it won't go away on my son's 93 850 GLT. I have been reading your posts on this subject and I have a question...What the Heck is a MOSFET?? Until now the only MOSFET I knew was a sound system....Thanks

It's a military acronym for someone who really likes Windows.

ECC fault code --updated

Re: ECC fault code --updated