Pinpoint Test G: Inaccurate Tachometer Indication
Instrumentation, Message Center and Warning Chimes
Pinpoint Tests
Pinpoint Test G: Inaccurate Tachometer Indication
Normal Operation
The PCM uses the Crankshaft Position (CKP) sensor to measure the engine rpm and sends the Instrument Cluster (IC) data over the High Speed Controller Area Network (HS-CAN) communication bus to command the tachometer gauge according to the data.
If the IC does not receive the engine rpm data from the PCM for 5 seconds or less, the IC defaults the tachometer to the last setting, based upon the last known good rpm message. If the IC does not receive the engine rpm data from the PCM for more than 5 seconds or if the data received is deemed invalid, the IC sets DTC U0100 in continuous memory and defaults the tachometer to 0 rpm.
NOTE: If DTC U0100 is set in the IC, other observable symptoms may be an inoperative speedometer, temperature gauge or odometer.
This pinpoint test is intended to diagnose the following:
- PCM concern
- IC
PINPOINT TEST G: INACCURATE TACHOMETER INDICATION
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G1 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 PCM DTCs recorded?
Yes
REFER to Computers and Control Systems Information.
No
GO to G2.
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G2 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 AU. Pinpoint Tests AU: DTC U0100
No
GO to G3.
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G3 OBSERVE THE TACHOMETER OPERATION
- Ignition ON.
- With the engine running, observe the tachometer while increasing the engine speed between 0 and 2,000 rpm.
- Ignition OFF.
- Does the tachometer begin at 0 rpm, increase with engine rpm then return to 0 rpm with the engine off?
Yes
GO to G4.
No
INSTALL a new IC. REFER to Instrument Cluster (IC) Instrument Cluster (IC). TEST the system for normal operation.
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G4 CARRY OUT THE IC TACHOMETER ACTIVE COMMAND USING THE SCAN TOOL
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: IC DataLogger.
- Select the IC tachometer (TACH) active command and command the tachometer in increments of 10%. Observe the tachometer. The tachometer should start at 0 and increase by approximately 700 rpm for each 10% increment.
- Does the tachometer increase by approximately 700 rpm for each 10% increment?
Yes
GO to G5.
No
INSTALL a new IC. REFER to Instrument Cluster (IC) Instrument Cluster (IC). TEST the system for normal operation.
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G5 CHECK THE PCM RPM SIGNAL INPUT
- Enter the following diagnostic mode on the scan tool: PCM DataLogger.
- Start the engine.
- Monitor the PCM engine speed PID (RPM) while operating the engine at 1,000 rpm, 1,500 rpm and 2,000 rpm.
- Does the PCM PID match the tachometer indication?
Yes
The tachometer is operating correctly at this time.
No
INSTALL a new IC. REFER to Instrument Cluster (IC) Instrument Cluster (IC). TEST the system for normal operation.
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