Pinpoint Tests AH: The Engine Over-Temperature Message Center Warning Indicator Is Never/Always On
Instrumentation, Message Center and Warning Chimes
Pinpoint Tests
Pinpoint Test AH: The Engine Over-Temperature Message Center Warning Indicator Is Never/Always On
Normal Operation
The PCM uses the Engine Coolant Temperature (ECT) sensor to measure the engine coolant temperature on the 6.4L diesel engine and the Cylinder Head Temperature (CHT) sensor on the 5.4L and 6.8L gasoline engines. The Instrument Cluster (IC) receives the engine coolant temperature data from the PCM over the High Speed Controller Area Network (HS-CAN) communication bus. The IC monitors the engine coolant temperature data received from the PCM and commands the engine over-temperature message center warning indicator on or off.
If the IC receives invalid engine coolant temperature data from the PCM for 5 seconds or less, the IC defaults the engine over-temperature message center warning indicator to the last setting, based upon the last known good temperature status message. If the IC does not receive the engine coolant temperature status message from the PCM or if the data received is deemed invalid for more than 5 seconds, the IC sets DTC U0100 in continuous memory and defaults the engine over-temperature message center warning indicator on. If the engine coolant temperature data is deemed invalid by the IC, the IC sets DTC U2023 and defaults engine over-temperature message center warning indicator on.
NOTE: If DTC U0100 is set in the IC, other observable symptoms may be an inoperative tachometer, temperature gauge or odometer.
This pinpoint test is intended to diagnose the following:
- PCM concern
- IC
PINPOINT TEST AH: THE ENGINE OVER-TEMPERATURE MESSAGE CENTER WARNING INDICATOR IS NEVER/ALWAYS ON
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AH1 RETRIEVE THE RECORDED DTCs FROM THE IC SELF-TEST
- Check for recorded IC DTCs from the self-test.
- Is DTC U0100 recorded?
Yes
GO to Pinpoint Test BD. Pinpoint Tests BD: DTC U0100
No
GO to AH2.
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AH2 RETRIEVE THE RECORDED DTCs FROM THE PCM KOEO SELF-TEST
- Check for recorded PCM DTCs from the Key ON Engine OFF (KOEO) self-test.
- Are any DTCs recorded?
Yes
REFER to Computers and Control Systems Information.
No
If the engine over-temperature message center warning indicator is never on, GO to AH3.
If the engine over-temperature message center warning indicator is always on, INSTALL a new IC. REFER to Instrument Cluster (IC) Instrument Cluster (IC). TEST the system for normal operation.
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AH3 VERIFY THE OPERATION OF THE DOOR AJAR MESSAGE CENTER WARNING INDICATOR
- Open the LH front door.
- Ignition ON.
- NOTE: If multiple warnings are present, the message center indicators rotate through each of the warnings. Allow the displays to rotate through each display while determining whether the door ajar message center warning indicator is active.
- Observe the message center or integrated display area of the IC.
- Is the door ajar message center warning indicator active?
Yes
The system is operating normally at this time. If the cylinder head temperature is high enough for the PCM to enter failsafe cooling mode, the PCM sets DTC P1285 and sends a command to the IC to illuminate the engine over-temperature message center warning indicator.
No
INSTALL a new IC. REFER to Instrument Cluster (IC) Instrument Cluster (IC). TEST the system for normal operation.
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