PCM Obituary
08-08-2019, 10:55 AM
#1
CF Veteran
Thread Starter
PCM Obituary
What started as a very rough running condition has turned into an engine harness rebuild. Now, I'm left with some strange voltages at the Powertrain Control Module. According to this thread, I should have 5v going to my sensors. Some only have 2.5v. All voltages supplied to the PCM through fused battery connections are accounted for. Any help is much appreciated- I'm handy with a multimeter but I've backed myself into the corner of a toasted PCM.
08-08-2019, 11:28 AM
#2
CF Veteran
Thread Starter
Here's what happened:
Turning into a parking lot, I cranked the steering wheel hard right and pulled into a spot. Shut the engine off. Bought a frozen pizza.
Went to start engine. Starts and runs terrible- black smoke out the tailpipe (rich exhaust) and sputtering. A very light throttle will get it to stay running.
Limped home. Once cooled off, the engine wouldn't start again without generous throttle pumping.
Check Engine Light shows codes P0113 and P0118, both "high" voltages for the engine coolant temp sensor and the intake air temperature.
Refreshed grounds. A more careful visual inspection revealed cooked wires feeding the camshaft sensor (stator for the coil) and coil supply harnesses. The coil + was definitely shorting out against it's ground supply. The insulation around the eyelets for those grounds looked pretty charred as well. I removed the wire loom and soldered in new wires with full insulation to the male plugs.
Both the ECT and IAT sensor harnesses have 2.5v at the terminal on the right side of the male plug. The ground-side of the terminal shares very little resistance with the negative battery terminal (grounds are now good...)
All other sensor harnesses, like the MAP, CPS, and TPS, show 5v at the right side of the male plug.
In this thread (and because I had cranked it hard right), CCKen mentions
I pulled the horn relay, checked the fuse, and bench-tested the clockspring with a rubber band holding it in alignment. Continuity between the contacts is there, and rotation of the inner spindle shows gradual, smooth change in resistance.
Diving in further, I started unplugging every sensor from the harness plugged into the PCM connector C1 with the black plug assembly (in case a sensor was causing the short). No luck. Jumped ahead and confirmed that the TAN/BLK wire from PCM pin#16 showed 2.5V, eliminating the possibility of a short between the PCM and sensor(s).
I can confirm (from the above-mentioned PCM check)
PIN 22 (Dark Green / Black) has 12.3v
PIN 2 (Dark Blue / White) has 12.2v
PIN 17 (Orange) has 5.2v
PINS 4, 6, 31, and 32 show minimal resistance to ground (-)
I've come to the conclusion that since all grounds and 12v power supplied are good, there are no shorts in the harness, and the 5v voltage that should be supplied by the PCM is 2.5v at the PCM pinout, that the PCM is not supplying the adequate voltage to a couple of the sensors, resulting in a "high voltage" return signal to the PCM.
Turning into a parking lot, I cranked the steering wheel hard right and pulled into a spot. Shut the engine off. Bought a frozen pizza.
Went to start engine. Starts and runs terrible- black smoke out the tailpipe (rich exhaust) and sputtering. A very light throttle will get it to stay running.
Limped home. Once cooled off, the engine wouldn't start again without generous throttle pumping.
Check Engine Light shows codes P0113 and P0118, both "high" voltages for the engine coolant temp sensor and the intake air temperature.
Refreshed grounds. A more careful visual inspection revealed cooked wires feeding the camshaft sensor (stator for the coil) and coil supply harnesses. The coil + was definitely shorting out against it's ground supply. The insulation around the eyelets for those grounds looked pretty charred as well. I removed the wire loom and soldered in new wires with full insulation to the male plugs.
Both the ECT and IAT sensor harnesses have 2.5v at the terminal on the right side of the male plug. The ground-side of the terminal shares very little resistance with the negative battery terminal (grounds are now good...)
All other sensor harnesses, like the MAP, CPS, and TPS, show 5v at the right side of the male plug.
In this thread (and because I had cranked it hard right), CCKen mentions
Diving in further, I started unplugging every sensor from the harness plugged into the PCM connector C1 with the black plug assembly (in case a sensor was causing the short). No luck. Jumped ahead and confirmed that the TAN/BLK wire from PCM pin#16 showed 2.5V, eliminating the possibility of a short between the PCM and sensor(s).
I can confirm (from the above-mentioned PCM check)
PIN 22 (Dark Green / Black) has 12.3v
PIN 2 (Dark Blue / White) has 12.2v
PIN 17 (Orange) has 5.2v
PINS 4, 6, 31, and 32 show minimal resistance to ground (-)
I've come to the conclusion that since all grounds and 12v power supplied are good, there are no shorts in the harness, and the 5v voltage that should be supplied by the PCM is 2.5v at the PCM pinout, that the PCM is not supplying the adequate voltage to a couple of the sensors, resulting in a "high voltage" return signal to the PCM.
08-08-2019, 01:06 PM
#3
CF Veteran
Thread Starter
For anyone else experiencing this symptom, I found this thread
https://www.jeepforum.com/forum/f11/...t-pcm-4356769/
Time for a new PCM, I think.
https://www.jeepforum.com/forum/f11/...t-pcm-4356769/
Time for a new PCM, I think.
08-08-2019, 10:58 PM
#4
CF Veteran
Join Date: Mar 2016
Posts: 3,520
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558 Posts
Year: 96
Model: Cherokee (XJ)
Engine: 4.0
For anyone else experiencing this symptom, I found this thread
https://www.jeepforum.com/forum/f11/...t-pcm-4356769/
Time for a new PCM, I think.
https://www.jeepforum.com/forum/f11/...t-pcm-4356769/
Time for a new PCM, I think.
but if you put up an excerpt of the relevant circuit diagrams, others my be able to point out any inconsistencies that you may have missed
a few heads is better than one, when ur stuck
08-09-2019, 10:35 AM
#5
Senior Member
I think it's clear: Your Jeep doesn't like Frozen Pizza!!
Sorry, I couldn't resist. As far as your problem, your year XJ is quite a bit newer than mine. You probably need to check every PCM wire for shorting ..or might be easier to get another used harness from the salvage yard ..and PCM. Not what you wanted to hear probably.
Sorry, I couldn't resist. As far as your problem, your year XJ is quite a bit newer than mine. You probably need to check every PCM wire for shorting ..or might be easier to get another used harness from the salvage yard ..and PCM. Not what you wanted to hear probably.
Last edited by Jeepwalker; 08-09-2019 at 10:37 AM.
08-10-2019, 07:23 AM
#6
CF Veteran
Check Engine Light shows codes P0113 and P0118, both "high" voltages for the engine coolant temp sensor and the intake air temperature.
Both the ECT and IAT sensor harnesses have 2.5v at the terminal on the right side of the male plug.
No luck. Jumped ahead and confirmed that the TAN/BLK wire from PCM pin#16 showed 2.5V, eliminating the possibility of a short between the PCM and sensor(s).
PIN 17 (Orange) has 5.2v
I've come to the conclusion that since all grounds and 12v power supplied are good, there are no shorts in the harness, and the 5v voltage that should be supplied by the PCM is 2.5v at the PCM pinout, that the PCM is not supplying the adequate voltage to a couple of the sensors, resulting in a "high voltage" return signal to the PCM.
Both the ECT and IAT sensor harnesses have 2.5v at the terminal on the right side of the male plug.
No luck. Jumped ahead and confirmed that the TAN/BLK wire from PCM pin#16 showed 2.5V, eliminating the possibility of a short between the PCM and sensor(s).
PIN 17 (Orange) has 5.2v
I've come to the conclusion that since all grounds and 12v power supplied are good, there are no shorts in the harness, and the 5v voltage that should be supplied by the PCM is 2.5v at the PCM pinout, that the PCM is not supplying the adequate voltage to a couple of the sensors, resulting in a "high voltage" return signal to the PCM.
How much volts at A15?
Is the engine running/starting poorly now?
08-10-2019, 07:39 AM
#7
CF Veteran
Because I don't believe you can simultaneously have
and
and 2.5V certainly seems normal. Was that with KOEO or at operating temperature?
Check Engine Light shows codes P0113 and P0118, both "high" voltages for the engine coolant temp sensor and the intake air temperature.
Both the ECT and IAT sensor harnesses have 2.5v at the terminal on the right side of the male plug.
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08-10-2019, 09:56 AM
#8
CF Veteran
Thread Starter
It does, but it's picky. I have to rearrange all the toppings evenly before it goes in the oven.
Right? It seems counterintuitive that the codes refer a "high voltage conditiion" when 2.5v is well below the 5v supply.
Key on only- I haven't been able to get the engine started again now that it has cooled off.
Last night I followed every wire from the PCM to its sensor and ground. I think 20 years of heat slowly fused the insulation on much of the harness together. Even after I removed the nylon and cloth tape, the wires had to be peeled apart and doing so stripped the wire bare in some spots. I think this is where the "High Voltage" nomenclature comes in. A few of the wires were probably shorting against each other, and the 5v supply wire (as well as sensor grounds) had enough exposed wire that it may have come in contact with sensor signals to the PCM.
So why the heat in the harness? Well, XJ engine bays are hot, but I suspect an issue with my coil. I had to replace it less than a year ago, and I wonder if the current to the old coil needed for a sufficient spark was more demand than the gauge of the wire. It's one of the wires that runs the entire length of the top-engine harness and may have been the extra heat needed to make ooze of the wire insulation.
Finally, I confirmed no continuity loss over the grounds and I'm going to roll with the 2.5v at the sensor signal pins. While 5v is supplied to the TPS (a potentiometer), I think I made an incorrect assumption that I should be seeing 5v at the sensor harnesses as well (though there are tutorials out there like this and this that say it should be close to 5v). Today I'm re-insulating the wires, bench-testing the coil, replacing the spark plugs, plug wires, and distributor rotor. I'll try to find some more research on the 2.5v versus 5v.
Key on only- I haven't been able to get the engine started again now that it has cooled off.
Last night I followed every wire from the PCM to its sensor and ground. I think 20 years of heat slowly fused the insulation on much of the harness together. Even after I removed the nylon and cloth tape, the wires had to be peeled apart and doing so stripped the wire bare in some spots. I think this is where the "High Voltage" nomenclature comes in. A few of the wires were probably shorting against each other, and the 5v supply wire (as well as sensor grounds) had enough exposed wire that it may have come in contact with sensor signals to the PCM.
So why the heat in the harness? Well, XJ engine bays are hot, but I suspect an issue with my coil. I had to replace it less than a year ago, and I wonder if the current to the old coil needed for a sufficient spark was more demand than the gauge of the wire. It's one of the wires that runs the entire length of the top-engine harness and may have been the extra heat needed to make ooze of the wire insulation.
Finally, I confirmed no continuity loss over the grounds and I'm going to roll with the 2.5v at the sensor signal pins. While 5v is supplied to the TPS (a potentiometer), I think I made an incorrect assumption that I should be seeing 5v at the sensor harnesses as well (though there are tutorials out there like this and this that say it should be close to 5v). Today I'm re-insulating the wires, bench-testing the coil, replacing the spark plugs, plug wires, and distributor rotor. I'll try to find some more research on the 2.5v versus 5v.
08-10-2019, 10:29 AM
#9
CF Veteran
08-11-2019, 07:25 AM
#11
CF Veteran
Finally, I confirmed no continuity loss over the grounds and I'm going to roll with the 2.5v at the sensor signal pins. While 5v is supplied to the TPS (a potentiometer), I think I made an incorrect assumption that I should be seeing 5v at the sensor harnesses as well (though there are tutorials out there like this and this that say it should be close to 5v). Today I'm re-insulating the wires, bench-testing the coil, replacing the spark plugs, plug wires, and distributor rotor. I'll try to find some more research on the 2.5v versus 5v.
08-11-2019, 12:51 PM
#12
CF Veteran
Thread Starter
That's correct- With key on, I get 2.5v when probing the wire, whether the sensor is plugged in or not. I get 2.5v at the IAC and ECT pinouts (15 and 16) on the PCM whether or not the PCM harness is plugged in. There is very good continuity between the PCM harness wires and the sensor harness wires, as well as their grounds.
08-11-2019, 05:47 PM
#13
CF Veteran
I would just reset the CEL. I'll bet it will clear and stay clear. My guess is that in the smoke the K167 circuit got B+ power, and K167 grounds like everything so those codes were triggered. I have surprise that a few more didn't go off.
However, if you are so inclined:
but IMO you kinda did that already.
However, if you are so inclined:
P0118-ECT SENSOR VOLTAGE TOO HIGH
When Monitored: With the ignition on and battery voltage greater than 10.4 volts.
Set Condition: The Engine Coolant Temperature (ECT) sensor circuit voltage at the PCM
goes above 4.98 volts for more than 3 seconds.
POSSIBLE CAUSES
INTERMITTENT CONDITION
ECT SENSOR SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE
ECT SENSOR INTERNAL FAILURE
ECT SENSOR SIGNAL CIRCUIT OPEN
SENSOR GROUND CIRCUIT OPEN
PCM
TEST ACTION APPLICABILITY
1 Turn the ignition on.
With the DRBIIIt, read DTCs.
Is the Good Trip Counter for P0118 displayed and equal to zero?
All
Yes → Go To 2
No → Go To 7
2 Turn the ignition off.
Disconnect the ECT Sensor harness connector.
Turn the ignition on.
Measure the voltage of the ECT Sensor Signal circuit in the ECT Sensor harness
connector.
Is the voltage above 5.2 volts?
All
Yes → Repair the ECT Sensor Signal circuit for a short to battery
voltage.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No → Go To 3
53
DRIVEABILITY - GAS
TEST ACTION APPLICABILITY
3 Turn the ignition off.
Disconnect the ECT harness connector.
Connect a jumper wire between the ECT Sensor Signal circuit and the Sensor ground
circuit in the ECT harness connector.
Turn the ignition on.
With the DRBIIIt, read the ECT voltage.
Is the voltage below 1.0 volt?
All
Yes → Replace the ECT Sensor.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No → Go To 4
4 Turn the ignition off.
Disconnect the ECT Sensor harness connector.
Disconnect the PCM harness connector.
Measure the resistance of the ECT Sensor Signal circuit between the ECT Sensor
harness connector and the PCM harness connector.
Is the resistance below 5 ohms?
All
Yes → Go To 5
No → Repair the ECT Sensor Signal circuit for an open.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
5 Turn the ignition off.
Disconnect the ECT Sensor harness connector.
Disconnect the PCM harness connector(s).
Measure the resistance of the Sensor ground circuit in the ECT Sensor harness
connector to ground.
Is the resistance below 5 ohms?
All
Yes → Go To 6
No → Repair the Sensor ground circuit for an open.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
6 If there are no possible causes remaining, view repair. All
Repair
Replace the Powertrain Control Module.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
7 WARNING: KEEP CLEAR OF THE ENGINE’S MOVING PARTS.
NOTE: The conditions that set the DTC are not present at this time. The
following list may help in identifying the intermittent condition.
With the engine running at normal operating temperature, monitor the DRBIIIt
parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set.
Review the DRBIIIt Freeze Frame information. If possible, try to duplicate the
conditions under which the DTC was set.
Refer to any Technical Service Bulletins (TSB) that may apply.
Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or
partially broken wires.
Visually inspect the related wiring harness connectors. Look for broken, bent, pushed
out, or corroded terminals.
Were any of the above conditions present?
All
Yes → Repair as necessary
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No → Test Complete.
When Monitored: With the ignition on and battery voltage greater than 10.4 volts.
Set Condition: The Engine Coolant Temperature (ECT) sensor circuit voltage at the PCM
goes above 4.98 volts for more than 3 seconds.
POSSIBLE CAUSES
INTERMITTENT CONDITION
ECT SENSOR SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE
ECT SENSOR INTERNAL FAILURE
ECT SENSOR SIGNAL CIRCUIT OPEN
SENSOR GROUND CIRCUIT OPEN
PCM
TEST ACTION APPLICABILITY
1 Turn the ignition on.
With the DRBIIIt, read DTCs.
Is the Good Trip Counter for P0118 displayed and equal to zero?
All
Yes → Go To 2
No → Go To 7
2 Turn the ignition off.
Disconnect the ECT Sensor harness connector.
Turn the ignition on.
Measure the voltage of the ECT Sensor Signal circuit in the ECT Sensor harness
connector.
Is the voltage above 5.2 volts?
All
Yes → Repair the ECT Sensor Signal circuit for a short to battery
voltage.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No → Go To 3
53
DRIVEABILITY - GAS
TEST ACTION APPLICABILITY
3 Turn the ignition off.
Disconnect the ECT harness connector.
Connect a jumper wire between the ECT Sensor Signal circuit and the Sensor ground
circuit in the ECT harness connector.
Turn the ignition on.
With the DRBIIIt, read the ECT voltage.
Is the voltage below 1.0 volt?
All
Yes → Replace the ECT Sensor.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No → Go To 4
4 Turn the ignition off.
Disconnect the ECT Sensor harness connector.
Disconnect the PCM harness connector.
Measure the resistance of the ECT Sensor Signal circuit between the ECT Sensor
harness connector and the PCM harness connector.
Is the resistance below 5 ohms?
All
Yes → Go To 5
No → Repair the ECT Sensor Signal circuit for an open.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
5 Turn the ignition off.
Disconnect the ECT Sensor harness connector.
Disconnect the PCM harness connector(s).
Measure the resistance of the Sensor ground circuit in the ECT Sensor harness
connector to ground.
Is the resistance below 5 ohms?
All
Yes → Go To 6
No → Repair the Sensor ground circuit for an open.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
6 If there are no possible causes remaining, view repair. All
Repair
Replace the Powertrain Control Module.
Perform POWERTRAIN VERIFICATION TEST VER - 5.
7 WARNING: KEEP CLEAR OF THE ENGINE’S MOVING PARTS.
NOTE: The conditions that set the DTC are not present at this time. The
following list may help in identifying the intermittent condition.
With the engine running at normal operating temperature, monitor the DRBIIIt
parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set.
Review the DRBIIIt Freeze Frame information. If possible, try to duplicate the
conditions under which the DTC was set.
Refer to any Technical Service Bulletins (TSB) that may apply.
Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or
partially broken wires.
Visually inspect the related wiring harness connectors. Look for broken, bent, pushed
out, or corroded terminals.
Were any of the above conditions present?
All
Yes → Repair as necessary
Perform POWERTRAIN VERIFICATION TEST VER - 5.
No → Test Complete.
08-11-2019, 06:54 PM
#14
CF Veteran
Thread Starter
That's something I forgot to menton- I can clear the CE light with my OBDII reader and it blinks off, then immediately back on. I've tried resetting the PCM by disconnecting the + cable and grounding it for five minutes as well as leaving the battery disconnected (on a float charge) overnight. Another couple of things that may be worth mentioning:
a) the battery temperature sensor wires show good continuity all the way to the PCM, and I can get a code to throw if I disconnect it.
b) I bench tested the coil and it checked out
c) Old spark plugs were coated in soot. I believe the sensor voltage is causing a very rich condition and the buildup probably happened when I limped it home.
d) Fuel pump runs for 1-2 seconds with key-on, about 48psi at the fuel rail with a slight dip to maybe 46psi when cranking.
e) Strong spark at the coil- not sure about the distributor cap though. Good condition, but I need to check the spark at night.
f) The BUS test, with the odometer button held during key-on, cycles 0-9 just fine
a) the battery temperature sensor wires show good continuity all the way to the PCM, and I can get a code to throw if I disconnect it.
b) I bench tested the coil and it checked out
c) Old spark plugs were coated in soot. I believe the sensor voltage is causing a very rich condition and the buildup probably happened when I limped it home.
d) Fuel pump runs for 1-2 seconds with key-on, about 48psi at the fuel rail with a slight dip to maybe 46psi when cranking.
e) Strong spark at the coil- not sure about the distributor cap though. Good condition, but I need to check the spark at night.
f) The BUS test, with the odometer button held during key-on, cycles 0-9 just fine
Last edited by alpine.adrenaline; 08-11-2019 at 06:56 PM.
08-11-2019, 09:05 PM
#15
CF Veteran