91 nissan truck, ECU under the seat. Never Failed.

90 Chevy Vette, ECU under hood. Its already ate two that i know of, who knows how many it ate the 10 years before i bought it

 

When the ECM went in my '92, I do think the problem was heat related.
When started cold, it ran fine until the engine warmed up to the point that the oil temp was about 160 -- at this point, the engine temp had been 180 for some time so it wasn't a open vs closed loop problem.
I got the serial-communications failure at that point.
But then, in Florida, it gets hot under the hood when the engine hasn't been run in a week -- let alone after the engine has been running.

After discussing this with Chris Petris, he also believed it was the fact the ECM was under the hood. He said he saw others fail in exactly the same way -- intermittent and after the engine warmed up.

I replaced the ECM with a GM refurbished one several years ago and haven't had a problem since.

Tom Piper

 

All the ECM's that I have worked with that were in the passenger compartment got a little warm just from operating, I don't know why GM thought it was a good idea to introduce even more heat to them. I would imagine that next to moisture, heat is the number one enemy of an ECM.

I'm trying to line up another ECM, the extremely overpriced POS that I recently bought worked for 1 day and then went completely dead. Put the old one in and car still runs, the ECM just interprets the signal from the CTS to be at 107-108* whenever the engine is running. Everything else is fine. Put the scanner on it and it says the same thing as the digital gauges. Zip now tells me that their ECM's are on a 2-3 week backorder so I may go to NAPA :ack

KC

 

If you want to double check the coolant temperature sensor, you can disconnect it and use a digital ohmmeter to measure it.
The shop manual has a chart that lists the readings for several temperature values.

You could have a defective sensor or the wiring to the sensor.

And, as long as we are on this subject, if you have access to the book "Corvette Fuel Injection & Electronic Engine Management" by Charles O. Probst, look on page76 Figure 4-46. It is interesting that the ECM switches the circuit that the ECT/CTS is connected to at 120* F.
I, too, noticed this several years ago when I made my own automatic circuit to turn the fans on at a lower temperature (I now have a custom chip that does it).
This switching of the circuit is completely transparent to the digital temperature display, but if you monitor the voltage on the sensor with a digital voltmeter, it acts just like the book says.

Tom Piper

 

I've replaced the CTS. Measured the resistance at the sensor and at the ECM harness at several different temperatures and it was always within a few ohms (sensor versus harness). Someone replaced the CTS at one time and wired in a new terminal end for it so I thought that was the prob; re-wired it and no luck still the same readings. Still betting on the ECM.
I'll look for that one. Although, I've hooked a scanner up to it and it (the CTS reading on the scanner) reads the same as the digital gauge, perhaps I'm not following what your saying. Thanks though for the suggestion.

KC

 

I really meant the comment about the Charles O. Probst book as an interesting side-note, not a solution to your problem.

I mentioned it because most would not expect that kind of behavior from the CTS/ECT sensor if they would monitor it with a digital voltmeter -- at exactly 120 degrees F, temperature rising, the voltage across the CTS would jump and almost double. And, with the temperature falling, the voltage would jump and decrease by about half.
And, looking at the digital readout on the dash, it would look exacly as you would expect -- a smooth transition in temperature.

The reason this happens is the ECM switches the circuit it is applyiing to the CTS at exactly 120 * F and also accounts for it internally. So, this is transparent to the running of the engine and the digital temperature readout.

Tom Piper

 

Wow I'm glad I found this post. I'm having the exact same problem now as is being described. Tom P, I wish you had PM enabled!

I have been working through a number of cascading problems that seem to be occurring one after the other or on top of each other.

I've spliced in a new ignition coil module connector, a new tach filter and coil/ign coil module. Got it started back up. But it had a very rough missing idle when in gear and stopped. Then a week of isolating an occassional 41 and 72 but mostly a 13 left O2 sensor. Pulled the O2 sensors yesterday and they were thick solid with carbon. So I re-installed the known good original set. Cleared the codes fired it up, and it was perfect (I thought) took a test drive running very well very smooth even at all the stops in gear. So I put it back in the garage and thought finally I solved the problem.

Yesterday I had it at the dealer to have the a/c serviced it seemed to have dumped its freon and was low. They couldn't find the leak so they refilled it and put a dye in. Going to monitor for a leak with a black light over the next day or so. So my a/c is working fine again. Everything seemed happy.

NO, last night going to the store I'm sitting at the light it starts to stumble recovers and I get an SES, Service ASR, SYS flashing a couple times, the back to the normal display then a LO appears and goes away. It is running terrible at the low idle position so I limp it back to the house. BTW, it runs fine when open it up.

I pulled the codes an yes now I'm getting another 41 with a 72. I'm pulling what hair I have left out. This is absolutely crazy.

So Tom, in your highly respected wisdom, it sounds to me like I'm experiencing the same problem that you experienced. Its fine cold but once it comes up to temp it intermittently loses communication with either the ECM and/or the EBTCM.

I took my knee bolster and brace off last weekend I could not find the CCM. I was thinking of a) trying to locate it to test the serial data line (although I don't have the special adapter) and perhaps clean the connections with contact cleaner spray. But I can't even find the daymn thing. I was thinking of going back over my grounds and pulling the ECM and spraying its connectors too. I'm at my wits end here.

So you think that this sounds like the same problem and replacing the ECM is mostly likely the solution.

Mine is also an early 93 with the old style ECM.

Please help.

Oh I should add too that I can talk to the CCM through the panel buttons using the jumpered DLC. I can clear the codes fine, and get a C12 afterwards. Also yesterday the dealer used their tech 1 to talk to it during the a/c service, they left the DLC cover off . Other than cycling through some of the other CCM test pages for example to cycle the courtesy lamp relay I'm making the assumption that the CCM is fine because it is allowing me to issue commands and monitor over that serial link.

 

My problem only manifested itself after the ECM had time to warm up from the under-hood temperature.

Replacing the ECM solved my problem (that was about 5 years ago).


Tom Piper

 

Hey Tom... so glad your around.

And BTW thanks for helping with the other problems. So having read what I've been experiencing, what I've changed/repaired, and with what is currently happening, do you think I'm in the ECM swap out boat?

 

Holy crap KC I have the same thing going on here. a '93 six speed <80k on the clock. I have gone thru ALL of the grounds. No avail. Tried the ecm in another car and it worked fine, albeit only tried it for a few minutes. Everything started after the head/cam swap. I guess it's better not to disturb the older girls, they get fussy.
digital guages go nutz, service asr light goes on. Motor floods. The grounds for the ccm and mst other guage/dash stuff is right next to the drivers/passengers foot on both sides of the car. You can reach back and feel it without removing the interior. They are right about under the hood release. I have a new ecm on the way Hopefully ti will cure what ails the car. IF not I'll look into the CCM as well. It would make more sense, as it is a systems wide failure.

 

The best thing you could do to try and pin down the problem is to use a good scan-tool and take a "snapshot" of the data when the problem happens. A snapshot usually consists of about 30 to 60 frames of data that can be graphed and analyzed. By triggering the snapshot when the problem happens, you have control of when the data is captured. On some scan-tools you can set it up to trigger when a particular trouble-code happens, on any trouble-code, or at your command.
I suggest trying this first in an attempt to prevent guessing.

However, I should mention, when my ECM was failing intermittently at operating temperature, I could not get a snapshot due to the failing of the serial-link. After much checking, I made an educated guess that the problem was the ECM, and fortunately I was correct.

With the symptoms you are having, I am guessing on the ECM.

Tom Piper

 

I hope an new ecm solves the electrical wackyness in this 93. Im out of Ideas.

 

Morning Tom, thanks for the info. I don't have a scan tool like that. What I did do this weekend which was quite a job I must say, was pulled the CCM out and tested continuity between the ECM D4 & D15 to the CCM E13 and F12. Continuity was good. Also ran the remainder of the diagnostic tests which included testing for a short or open circuit. I also pulled the ETBCM connector and tested terminals 3 & 4 for continuity, voltage and resistance all were well within desired parameters.

The I cleaned all the connectors and pins with contact cleaner and blew them clean with compressed air, then re-assembled everything, cleared the codes and started it up. I still have the slight miss at low load idle, no codes yet but I didn't drive it much and it didn't have a chance to heat soak.

Since I know now my connections are good, the next step is to get an ECM on the way in.

thanks again.

 

Well that was it. Replaced the ECM and the problem went away. I noticed that in replacing the existing ECM it was still major hot to the touch while removing it and it had been sitting for over an hour after only having driven home from work about 5 miles. After swapping the PROM, I noticed the familiar scent (stench) of burned components. Some chip or component was either cooking or already cooked in there. The replacement barely gets warm.

Finally! This one was really getting to me, all the detailed troubleshooting and focused parts replacement. But I did it....

and not without a big THANK YOU to all those who helped especially Tom and Andy. You guys are simply great!

Thank you.

 

Yep I did something similar, since my problem was sourced around grounds/ECT I simple bit the bullet and replaced them (A pain I Know). That way I can be certain that the wire is MAINTAINING continuity. This did not fix the intermittent problem so I got the new ecm, put in a fresh set of plugs (had leaky injectors) and put 60+ miles on it. So far so good. IM going to call the guy and have him come get it. That way Murphy's law can enact itself and truly test it's state of repair