Check engine light -- p0ac4

[BethC]

Good Morning all -

I tried to search, and haven't found others with this code, but I may have missed it. This morning I started out fine and drove the 3ish miles to the gym. Parked the car for a bit less than an hour and then came back and when I restarted the car the check engine light stayed on at start up. I called On Star as I drove to school and they said it was a fault in the propulsion system and gave me the code p0ac4. She said I should go to the dealer within 24 hours. I will call them shortly and perhaps my students can teach themselves this afternoon so I can take it in!

Any thoughts?

[?'smyvolt]

Good Morning all -

I tried to search, and haven't found others with this code, but I may have missed it. This morning I started out fine and drove the 3ish miles to the gym. Parked the car for a bit less than an hour and then came back and when I restarted the car the check engine light stayed on at start up. I called On Star as I drove to school and they said it was a fault in the propulsion system and gave me the code p0ac4. She said I should go to the dealer within 24 hours. I will call them shortly and perhaps my students can teach themselves this afternoon so I can take it in!

Any thoughts?

I have had several Check Engine Light (CEL) issues, all of which did not turn out to be what they were initially thought to be. What I have found is that if you go through 3 cycles of operating the car without any new code being generated, on the 4th start, the code goes away. If the problem is a persistent, recurring problem, I am told, the code will be renewed each time the underlying problem is detected. If it is not a persistent problem it is called an Historical problem and is stored in the car's memory.

Don't know if this helps.

#565

[WopOnTour]

Good Morning all -

I tried to search, and haven't found others with this code, but I may have missed it. This morning I started out fine and drove the 3ish miles to the gym. Parked the car for a bit less than an hour and then came back and when I restarted the car the check engine light stayed on at start up. I called On Star as I drove to school and they said it was a fault in the propulsion system and gave me the code p0ac4. She said I should go to the dealer within 24 hours. I will call them shortly and perhaps my students can teach themselves this afternoon so I can take it in!

Any thoughts?

Well there MUST have been another DTC. P0AC4 isnt really even considered a "fault" code, as it will automatically set in the Engine Control Module (ECM) whenever some other system significant fault s detected within either of the Hybrid Powertrain Control Modules (HPCM1/2). Since the ECM is really the only module permitted to turn "ON" the Check Engine/ Malfunction Indicator Light due to OBD2 regulations. When the HPCM detects a system problem it essentially "tells" the ECM to set the P0AC4, basically JUST to turn on the MIL. So this code is always set in combination with some other DTC.
Did Onstar even mention another code? Did you write them down?
WopOnTour

[bitguru]

Well there MUST have been another DTC. P0AC4 isnt really even considered a "fault" code, as it will automatically set in the Engine Control Module (ECM) whenever some other system significant faults ... So this code is always set in combination with some other DTC.
Did Onstar even mention another code?

OnStar did not mention it, however the other code was apparently P1E27.


DTC P1E27: Auxiliary Transmission Fluid Pump Control Module Hybrid/EV Battery System Voltage High Voltage

The power inverter module, often referred to as the drive motor generator power inverter module, contains three motor control modules and the hybrid powertrain control module. Two of the motor control modules operate their respective drive motor generator based upon power inverter module commands. The third motor control module controls the auxiliary transmission fluid pump motor. Each drive motor control module monitors its internal high voltage sensor for correct operation, no external circuits are involved. The motor control modules and the hybrid powertrain control module are part of the power inverter module and are not serviced separately.

Conditions for Setting the DTC P1E27: The motor control module detects High Voltage greater than 425 V.

Diagnostic Aids: This DTC may set due to low 12 V system voltage.

1. Verify that DTC P0562 is not set. (If DTC is set, refer to ....)
2. If the DTC is set, program the T6 power inverter module. If the DTC resets, relplace the T6 power inverter module.

Recommendation/Instructions: These DTC's may be set on a vehicle that exhibits a low 12 volt system condition. If the vehicle has any dtc's related to low 12 volts, or it has experiences a known low 12 volt condition, do not replace the Power Inverter Module. Address and correct the low 12 volt condition prior to attempting diagnosis of dtc's P1E27, P06E7, P150D or P150E.

[?'smyvolt]

Conditions for Setting the DTC P1E27: The motor control module detects High Voltage greater than 425 V.

Bitguru,

425 volts or 245 volts?

#565

[bitguru]

425 volts or 245 volts?

425 is what it says, but I can't vouch for its accuracy.

[Stilgar99]

bitguru,
Where are you getting all the DTC info?

Stilgar

[?'smyvolt]

Seems like 245 would be the right answer, but I dunno....

[?'smyvolt]

425 is what it says, but I can't vouch for its accuracy.

The reason I am so interested is the problem I have been having with Check Engine Light (CEL) codes and my SPX Voltec 240 volt charger (see http://gm-volt.com/forum/showthread....oltec-Problems). I have just about concluded that the problem comes when there is a surge or a sag in power and it gets outside the +/- parameters of the car's built in circuit protection limits. If the car turns off, then that might cause the SPX to think it is broken and start flashing red lights. Wish somebody knew the acceptable + and - voltage input limits.

#565

[WopOnTour]

OnStar did not mention it, however the other code was apparently P1E27.

What makes ou think it was P1E27 if Onstar didnt say?
OR
Did you have it scanned at a dealer already? (apparently so as I assume this is where you got the DTC diagnostic document)

WEll as the chart indicates, theis code can set falsly if the 12V battery was run down to the point where the Volt wouldnt "start" (be powered ON) But if that wasnt the case, Step 2. of the procedure should be followed, begnning with reflashing the PIM in order to reset the internal diagnostic executive. If the DTC persists the PIM will need to be replaced.
Please let us know what ends up being done to rectify the issue.
WopOnTour