Pinpoint Test G: Incorrect Speedometer Indication
Instrumentation, Message Center and Warning Chimes
Pinpoint Tests
Pinpoint Test G: Incorrect Speedometer Indication
Normal Operation
The Instrument Cluster (IC) receives the vehicle speed data from the PCM over the High Speed Controller Area Network (HS-CAN) communication bus. The vehicle speed data originates with the Output Shaft Speed (OSS) sensor. The OSS sensor sends the output shaft speed data to the Transmission Control Module (TCM). The TCM provides the output shaft speed data to the PCM over the HS-CAN bus. The PCM uses the messaged OSS data along with the tire size and axle ratio configuration stored in the Vehicle Identification (VID) block to generate the vehicle speed data sent to the IC. The IC monitors the vehicle speed data input from the PCM and commands the speedometer with a corresponding movement of the pointer.
The IC provides a tolerance which biases the speed indication and allows the gauge to display between 3% lower and 7% higher than the actual vehicle speed. This means that with an actual vehicle speed of 96.6 km/h (60 mph), the speedometer may indicate between 93.7-103.3 km/h (58.2-64.2 mph). Other factors that could potentially affect the speedometer accuracy are incorrect tire size, tire size configuration and axle ratio configuration.
If the OSS message is missing or if the OSS sensor fails, the PCM uses a vehicle speed input from the ABS module over the HS-CAN bus combined with the tire size and axle ratio configuration in the VID block to generate the vehicle speed data sent to the IC.
If the OSS message is missing or if the OSS sensor fails and the ABS vehicle speed message is missing, the IC defaults the speedometer to 0 rpm.
If the vehicle speed message is missing or deemed invalid for greater than 5 seconds, the IC sets DTC U0100 and defaults the speedometer to 0 rpm.
This pinpoint test is intended to diagnose the following:
- Tire size configuration
- Axle ratio configuration
- PCM concern
- IC
PINPOINT TEST G: THE SPEEDOMETER IS INACCURATE
NOTE: It is important to confirm that the speedometer is inaccurate by either comparing vehicle speed against mile markers on highways (where available) or by comparison using a second vehicle before beginning diagnostics.
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G1 OBSERVE THE SPEEDOMETER POINTER POSITION
- Observe the speedometer while driving the vehicle at various speeds and stopping frequently.
- Does the speedometer begin at 0 km/h (0 mph) and fully return to the 0 km/h (0 mph) position when the vehicle is stopped?
Yes
GO to G2.
No
INSTALL a new IC. REFER to Instrument Cluster (IC) Instrument Cluster (IC). TEST the system for normal operation.
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G2 CHECK FOR CORRECT AXLE RATIO AND TIRE SIZE CONFIGURATION
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: Module Programming .
- Select programmable parameters and confirm that the axle ratio and the tire size is correctly configured.
- Is the axle ratio and tire size correctly configured?
Yes
GO to G3.
No
CONFIGURE the axle ratio or tire size as required. TEST the system for normal operation.
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G3 RETRIEVE THE RECORDED DTCs FROM THE KOEO PCM 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
GO to G4.
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G4 RETRIEVE THE RECORDED DTCs FROM BOTH THE CONTINUOUS AND ON-DEMAND IC SELF-TESTS
- Check for recorded IC DTCs from the continuous self-test.
- Is DTC U0100 recorded?
Yes
GO to Pinpoint Test AT. Pinpoint Tests AT: DTC U0100
No
GO to G5.
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G5 CARRY OUT THE IC SPEEDOMETER ACTIVE COMMAND USING THE SCAN TOOL
- Enter the following diagnostic mode on the scan tool: IC DataLogger .
- Select the IC speedometer active command (SPD_IND) and scroll in 10% increments.
- Does the speedometer start at 0 km/h (0 mph) and increase by 19.3 km/h (12 mph) for each 10% increase commanded?
Yes
GO to G6.
No
INSTALL a new IC. REFER to Instrument Cluster (IC) Instrument Cluster (IC). TEST the system for normal operation.
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G6 CARRY OUT THE IC) DEALER TEST MODE
NOTE: This step may require the use of an assistant to monitor and record the IC self-test and the speedometer readings.
- Enter the IC dealer test mode with the Key ON Engine Running (KOER) by pressing and holding the odometer/trip odometer reset button (base IC) or the message center switch RESET button (message center IC) while starting the engine. Scroll through the displays until VEHICLE SPD is displayed.
- Drive the vehicle at varying speeds.
- Monitor the vehicle speed input with the speedometer reading.
- Do the self-test vehicle speed input values match the speedometer indication?
Yes
GO to G7.
No
INSTALL a new IC. REFER to Instrument Cluster (IC) Instrument Cluster (IC). TEST the system for normal operation.
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G7 CHECK THE PCM VSS SIGNAL INPUT
NOTE: This step may require the use of an assistant to monitor and record the IC dealer test mode and the speedometer readings.
- Enter the following diagnostic mode on the scan tool: PCM DataLogger .
- Select the PCM vehicle speed (VSS) PID and monitor the PID while driving the vehicle at 32 km/h (20 mph), 64 km/h (40 mph) and 97 km/h (60 mph).
- Does the speedometer indicate between 31-34 km/h (19-21 mph), 63-69 km/h (39-43 mph) and 93-103 km/h (58-64 mph) at the 3 PCM PID values?
Yes
The speedometer 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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