Strange issue with intermittant Temp Sensor Signal, E40 PCM in 2006 GTO(replaced ECM)

[mm_n_p]

Back story - I have been having an intermittent temp sensor signal issue that a reflash of the ECM will fix temporarily. When the signal fails, my gauge drops to cold and fans quit working. I'm not sure now this is related, but the A/C quits working in the car as well. When this issue is present, I can scan these signals and all seems to be operating as normal, according to what I'm seeing in the scanner. Even though the gauge shows cold, ECM sees temp as normal and I can also turn on/off the AC, Engine fans etc via the "Vehicle Controls" console in VCM scanner.

Current Status - Since I found this issue I took a semi educated guess and was convinced it was in the ECM, reason being...I could do a reflash and all would work fine for a random amount of time. I could be driving down the road just 15 miles after a reflash and it would fail, or it may take several days and hundreds of miles. No rhyme or reason that I could pinpoint. With that said, I replaced with a NEW ECU a week ago and thought it was fixed only to find out yesterday that this is not the case as my temp gauge dropped to Cold again on the way home from work, engine fans shut off and A/C quit working. I didn't have my laptop on me but was fairly close to the house and once I got home, relfashed and all is good again (for now)

Which way do I go now? Is it possible that its the BCM or even PIM? if so, why does a reflash of the ECU temporarily fix it? I cant imagine this the case but Is there any chance at all that my MPVI Pro unit is leaning towards flaking out? I paid to upgrade it a couple weeks ago but held off since this issue started because now that my wife is working, the Goat has become my daily and so I keep my MPVI in the car in the event I need to perform a reflash.

Thanks in advance for any input
-Steve

Next time this happens, I'm going to try a battery disconnect. Wont fix it but may tell me a little more about what is temporarily fixing the problem. I'm also working on sourcing schematics to help troubleshoot but I cant imagine the problem being external to a controller.

[blindsquirrel]

Instrument Cluster Description and Operation

The powertrain control module (PCM) sends serial data to the body control module (BCM) along the primary serial data bus circuit. Serial data is then sent to the instrument cluster along the secondary serial data bus circuit. The following data is read by the instrument cluster, which then indicates the status as appropriate on the multifunction display (MFD) and/or cluster warning indicators:
? Oil pressure
? High temperature
? Check engine (powertrain)

A powertrain interface module (PIM) is required to convert the serial data generated by the (PCM) into serial data that is compatible with the BCM.

Engine Coolant Temperature Gage
The instrument cluster receives engine coolant temperature information from the powertrain control module (PCM) via the serial data bus normal mode message. The PCM receives engine coolant temperature information from the engine coolant temperature (ECT) Sensor. The ECT Sensor is a thermistor mounted in the engine coolant stream. Low engine coolant temperature produces a high sensor resistance, while high engine coolant temperature causes a low sensor resistance.

Fuel Gage
The fuel sender unit provides a percentage value to the instrument cluster based on its position relative to the fuel level. The percentage value will vary between 0 percent with no fuel in the tank and 100 percent with a full tank. The instrument cluster drives the fuel gauge pointer to the appropriate position.

PRNDL Display
The IPC displays the selected gear position as determined by the PCM. The IPC receives a message from the PCM indicating the gear position. When the position of the transmission selector is changed, a large icon is displayed on the MFD in conjunction with the PRND321 constant icon at the bottom of the MFD. The square box around the designated gear letter moves according to what gear is selected on the gear selector.

Speedometer
The instrument cluster receives vehicle speed information from the Powertrain Control Module (PCM) via the speedometer signal circuit. The PCM pulses this circuit to ground. The number of pulses varies with tire size. The PCM receives vehicle speed information from the vehicle speed sensor located in the transmission assembly. Voltage is produced by the speed sensor and is fed to the PCM, which filters and shapes the signal. The PCM then counts the number of pulses received in a given time to determine the vehicle speed. Once the PCM has calculated the vehicle speed, it then pulses the speedometer signal circuit to ground. This causes the 12 volts at instrument cluster to be pulled down to less than 0.5 volt. The instrument cluster then determines the vehicle speed and the miles/kilometers travelled from the number of pulses it receives.

Tachometer
The instrument cluster receives the engine speed (RPM) information from the PCM via the tach signal circuit. The PCM pulses the circuit to ground and the instrument cluster counts the number of pulses to determine the speed (RPM) of the engine

[mm_n_p]

good info which I hadn't found yet in hours of google searches - Thank You

So, I'll summarize my issues (that I have noticed) and try to pinpoint how each is controlled using what I think I'm reading above and think I already know (im electrically slow)

Temp Gauge
a. signal from sensor is direct to PCM - low temp = high resistance
b. Gauge display is driven by serial data directly from PCM? Not BCM - This I wasn't aware of.

No engine fans
a. PCM "THINKS" engine is cold and controlled by PCM (Working as designed )

Vehicle running rich -
a. fast idle, hard restart when warm which is still due to false temp signal and all controlled directly by PCM.

If the above is correct it sounds like PIM/BCM is not involved in any of those issues. It just doesn't answer how do I see a normal temp signal when I use VCM Scanner, but PCM itself doesn't seem to process it that way? I'm just not grasping that yet and am going to have to see this again for myself, for the 3rd time, next time it happens - maybe I'm overlooking something.

As far as my A/C not working, I believe (could be mistaken) the user input signal is processed by the BCM but clutch is controlled by the PCM which would make it the only problem I have that involves a controller other than the PCM. Just FYI - I can control the clutch using the VCM control console when this problem arises.

Just to reiterate - All of the above is temporarily fixed with a PCM Re-Write

I noticed you attached a gauge test procedure - I should be able to do this as soon as my MDI gets here (Saturday) but I don't think this is the problem. Besides the no A/C issue, everything else seems to revolve around a faulty temp sensor signal of some sort.

-Steve

[blindsquirrel]

This is either a gauge issue inside the IPC or a coolant temp sensor (wiring/connector) issue. If it were something flaky with the data stream (wiring, PIM, BCM) it would take out all the gauges. I can't see how there could be anything that would kill only the coolant temp signal and not also take out all the other serial data.

When you know it's working right, watch the coolant temp in the scanner and unplug the ECT, see if it defaults to some plausible number other than -40*. I would also be tempted to backprobe the ECT pins and monitor that while waiting for it to glitch out again.

[Asylumwarp]

So if your IPC is bad, I can clone the mileage and info from one cluster to the other, saving your mileage, programming, vin# etc and not require a tech 2. I repair the center lcd problems all the time now.

[mm_n_p]

This is either a gauge issue inside the IPC or a coolant temp sensor (wiring/connector) issue. If it were something flaky with the data stream (wiring, PIM, BCM) it would take out all the gauges. I can't see how there could be anything that would kill only the coolant temp signal and not also take out all the other serial data.

When you know it's working right, watch the coolant temp in the scanner and unplug the ECT, see if it defaults to some plausible number other than -40*. I would also be tempted to backprobe the ECT pins and monitor that while waiting for it to glitch out again.

I think you are right, after doing some research I found out that the AC disables if the PCM doesn't know what the ECT temperature is. I will verify all wiring. signals and sensor is in good condition before I pursue anything else further. I have a funny feeling that I may have way over thought this.

I'll update when I get something solid to note.

[mm_n_p]

So if your IPC is bad, I can clone the mileage and info from one cluster to the other, saving your mileage, programming, vin# etc and not require a tech 2. I repair the center lcd problems all the time now.

this is good info to have, You wouldn't by chance be able to clone BCM's as well, would you. I would like to have a spare PIM, BCM and IPC on hand since these parts are becoming scares.

[blindsquirrel]

Well, if the glitch affects the fan operation and the way the engine runs, it by definition can't be an IPC/gauge or data stream problem. The gauge or the PIM/BCM can't tell the ECM what to do, only the other way around.

And I left out some details when I said "backprobe the ECT pins and monitor that while waiting for it to glitch out again". Monitor voltage between those two pins with a DVOM, while driving if possible. Sensor unplugged or otherwise open circuit you should read ~5v (max low temp), shorted together/jumpered (yes, you can stick a jumper in there and see if it goes full hot, won't hurt anything) it should read ~0v.

[blindsquirrel]

If you can fight your way through the TIS2000 software install and get it working, you'll be able to program your own BCMs matched to your VIN with your MDI clone thing.

[5ft24]

The GTO's have a very common issue with the harness behind the glove box rubbing and chaffing and causing all kinds of weird issues. I would check that before dropping the cash for a BCM or PIM

[WOODS83X]

Just had this same problem with my 06 trailblazer as with e40. It turned out to be the wire broke about a 1/8 inch from the plug. Pulled on each wire a little and one stretched letting me know it was broke inside making contact sometimes. Hope this may help.

[mm_n_p]

Hey, I didn't realize I had so many responses, I guess I missed the notifications but non the less all good input and I will take into consideration as I continue to trouble this issue.

With all that aside, today was the first day that the issue arose since the last time that posted and wanted to respond to blindsquirrel's suggested tests.

1. I was not unable to capture voltage readings by pack probing at the moment that it failed as it takes quite some time before failure and I'm daily driving putting about 60 miles a day on it. On top of that, I don't have a DVM with any kind of recording capacity, if necessary to isolate this issue, I will find a way though.


2. With that said, I was able to back probe the ECM and read voltages with the vehicle currently experiencing the ECT related issues as well as capture some other info using the GTO's build in special menu AND Scanner readings. Here are my current findings..

a. As before, gauge is at "COLD" level, vehicle is hard starting when hot (sometimes require full pedal).
b. GTO special menu access in cluster - Coolant Temp = 419*
c. Scanner - ECT (SAE) reads normal operating temperature when key on and run. When ECT is unplugged it reads -40 which I believe is normal.
d. Scanner - ECT (??) key on can ready anywhere from 68* to 181* from what I have seen , engine running is about 198 but not smooth and not consistant with ECT (SAE) so not sure where this value is coming from(see scan below)
e. Voltages, ECT sensor plugged in and back probed at ECM - GB wire (pin 52) 4.1 vdc / Y wire (pin 55) 2.634 vdc
f. Voltages, ECT sensor unplugged and back probed at ECM - GB wire (pin 52) 4.1 vdc/ Y wire (pin 55) 5.04 vdc
g. Ohm reading across ECT sensor seems normal with a steady drop in value as engine slowly cools off.

Now I haven't done it yet, but I can guarantee that simply uploading my last tune will temporarily fix this problem, not sure how that is, I just know it has worked every time previously.

UPDATE: I don't have to reflash ECM , I just tried disconnecting the battery for 30 seconds and all seems to be working as normal again.

Also, I was mistake about the fans when this issues arises - the seem to be working as normal.

Thanks again
-Steve



Ect Troubleshoot.Layout.xml
ECT Troubleshoot.hpl

Adding responses to other posts:

The GTO's have a very common issue with the harness behind the glove box rubbing and chaffing and causing all kinds of weird issues. I would check that before dropping the cash for a BCM or PIM

I did look into this as I researched and found many complaints related to this online. I was unable to see any damage to any sheathing or wires going to the BCM after pulling out my glove box to inspect. I actually pulled BCM out to get a good look.

Just had this same problem with my 06 trailblazer as with e40. It turned out to be the wire broke about a 1/8 inch from the plug. Pulled on each wire a little and one stretched letting me know it was broke inside making contact sometimes. Hope this may help.

I actually considered this as I did break this sensor installing my headers and replaced with a new one so its likely. Did your broken wire cause the same issues I am experiencing, it just seems unlikely that an intermittent open in that circuit would cause these issues until a reflash of the ECM but that's just me thinking outloud.

If you can fight your way through the TIS2000 software install and get it working, you'll be able to program your own BCMs matched to your VIN with your MDI clone thing.

I'm sure I can fumble around until I figure it out - its just been sitting in the box so I guess I'll get it out and load the latest firmware in it and start checking it out as I search for a BCM. I take it, that I would have to get a new BCM?

[blindsquirrel]

If this was in my bay, I would want to see several data sources at once, since right now you don't know which one to believe. I would want to watch the same voltage the ECM is reading: DVOM red to pin 55/YEL, black to pin 52 GY/BK (checking each wire to GND isn't really useful here, and ohms is especially un-useful), and get a sense of what the range of voltage is when it's working as it should. And what the ECM thinks it is in VCM Scanner. When the gauge drops to 'cold', what changes? Does the DVOM reading go to ~5v (which would indicate an open ckt somewhere between ECM & ECT) but the scanner temp only go from 180* to 130*?

To monitor it long-term run temporary wires from the ECM at 52 & 55, through the firewall into the interior, connect your DVOM there where you can look at it while driving. Watch it a while and you'll learn to recognize what's normal. What does the scanner say when the gauge is at [x]? What's the DVOM voltage when the scanner says [y*]?

That's a very strange log, not sure what to make of that. Does ECT(SAE) always-always read 180* (except when it goes to -40?) Did you unplug the sensor at the end?

[mm_n_p]

I will setup to monitor between the ECT source/reference pins on the ECM - as you have suggested. I would really have to record this if I want to catch it when it happens as I have yet to catch the gauge actually drop. Up to this point I have only noticed it after it had already dropped sometimes by high idle at the next stop light which will cause me to look at my gauge. Maybe it will show some intermittent voltage issues that happen prior to the failure, that the gauge doesn't reflect.

I have only ever monitored ECT (not SAE) in my scanner until yesterday when I noticed the erratic behavior and decided to try ECT (SAE) which in that log reflects a steady value that seemed more accurate at the time, I'm just not sure where that value is coming from.
ECT (not SAE) was actually starting to smooth out again by the time I had actually saved that log. The log just before that, (which did not get saved) ECT temp value was switching between 70/180 degrees key on/run and when vehicle was running it was switching between about 160/180 degrees, unsure of switching frequency when running but fairly certain it was sub 1 second intervals. I will capture better data next time this happens.

I did disconnect the ECT sensor when temperature value went to -40 in the log.

[blindsquirrel]

All logs are automatically saved, look in Documents/HP Tuners/VCM Scanner/Logs folder.

I would be logging all the time, every drive. If you run short of disk space or something you can delete the ones afterward where nothing happened.

[iom2010camaro2ssrs]

Do you have a stock coolant thermostat? I have a 160 deg thermostat that was done with my initial supercharger install in 2010 on a 5th Gen Camaro that had the same symptoms. Since then I've seen it on numerous Camaros and GTOs could easily have the same ECM diagnostic that triggers it. A bad stock thermostat could do the same thing. I chased the problem for a few years until somebody brought up the correlation.

The P0128 Coolant Thermostat (Coolant Thermostat below regulating temperature) DTC has to be turned to "do not report" and the issues will permanently disappear.


When it happened I would sometimes get the code, sometimes not.... but I would get "AC off due to high temp" error and all my center console gauges would stop working. Anything that would reset the ECM would temporarily clear it..... reflash the ECU, battery disconnect, ECU disconnect, etc.

?.ASLO when this was happening, I too could scan my engine coolant temp and other temps via my Aeroforce OBDII gauges and everything was good! Hope this helps!

[blindsquirrel]

Do you have a stock coolant thermostat? I have a 160 deg thermostat that was done with my initial supercharger install in 2010 on a 5th Gen Camaro that had the same symptoms. Since then I've seen it on numerous Camaros and GTOs could easily have the same ECM diagnostic that triggers it. A bad stock thermostat could do the same thing. I chased the problem for a few years until somebody brought up the correlation.

The P0128 Coolant Thermostat (Coolant Thermostat below regulating temperature) DTC has to be turned to "do not report" and the issues will permanently disappear.


When it happened I would sometimes get the code, sometimes not.... but I would get "AC off due to high temp" error and all my center console gauges would stop working. Anything that would reset the ECM would temporarily clear it..... reflash the ECU, battery disconnect, ECU disconnect, etc.

?.ASLO when this was happening, I too could scan my engine coolant temp and other temps via my Aeroforce OBDII gauges and everything was good! Hope this helps!

That sure does sound like the same issue. From other threads (Google "site:hptuners.com+p0128") it looks like it'd be a good idea to kill P0116 as well, some still had the problem after disabling just P0128.

[mm_n_p]

I want ahead and -no reported- p0128 after I read this post and researched it further only to find several had the exact same issue. Problem is, now I?m still monitoring everything and not sure if issue will come back.

Im fairly certain the problem has been identified and half tempted to just pull my equipment out of the car so that I can have it back without a seat full of equipment and wires, lol.

If I don?t report back then all is well and greatly appreciate all of the help from you gentlemen.

[mm_n_p]

That sure does sound like the same issue. From other threads (Google "site:hptuners.com+p0128") it looks like it'd be a good idea to kill P0116 as well, some still had the problem after disabling just P0128.

I was looking at killing the P0116 after reading this and was wondering if I should get the p0117 as well?

Just for the record... I have a 180* stat

[blindsquirrel]

No, just P0116. 117 & 118 are detecting open or shorted. Those are things you'd probably want to know about and will legitimately affect the way it runs, none of that "range/performance" mystery algorithm analysis...