Possible Causes

PCM
instrument cluster

INACCURATE SPEEDOMETER READING - PINPOINT TEST REFERENCE

PINPOINT TEST 4		INACCURATE SPEEDOMETER READING
STEP	INSPECTION		ACTION
1	RETRIEVE THE RECORDED DTCs FROM BOTH THE CONTINUOUS AND ON-DEMAND PCM SELF-TESTS Retrieve the recorded DTCs from the PCM continuous and on-demand self-tests. Are any DTCs retrieved?	Yes	See DIAGNOSTIC TROUBLE CODE (DTC) INDEX - POWERTRAIN CONTROL MODULE (PCM) , .
1		No	Go to next step.
2	RETRIEVE THE RECORDED DTCs FROM BOTH THE CONTINUOUS AND ON-DEMAND INSTRUMENT CLUSTER SELF-TESTS Retrieve the recorded DTCs from the instrument cluster continuous and on-demand self-tests. Is DTC U0294 retrieved?	Yes	Clear the DTCs. Repeat the self-test. If DTC U0294 is retrieved again, go to step 5. For all other instrument cluster DTCs, See INSTRUMENT CLUSTER DIAGNOSTIC TROUBLE CODE (DTC) INDEX , .
2		No	Go to next step.
3	MONITOR PCM VEHICLE SPEED SIGNAL (VSS) PIDs NOTE: This step may require the assistance of a second person to monitor and record the scan tool data. Select, monitor and record the PCM PID VSS while driving at various different speeds. Compare the VSS PID values with the speedometer reading. Do the values on the speedometer match the PCM PID values?	Yes	Go to step 5.
3		No	Go to next step.
4	CARRY OUT THE INSTRUMENT CLUSTER GAUGES ACTIVE COMMAND USING THE SCAN TOOL Key ON engine OFF (KOEO). Enter the following diagnostic mode on the scan tool: Instrument Cluster Active Command Select the instrument cluster gauges active command. Select and scroll the speedometer 20%, 50% and 70%. Does the speedometer indicate approximately 24 mph at 20%, 60 mph at 50% and 84 mph at 70%?	Yes	Go to next step.
4		No	Go to step 6.
5	CHECK FOR CORRECT PCM OPERATION Disconnect all the PCM connectors. Check for: corrosion damaged pins pushed-out pins Connect the all the PCM connector and make sure they seat correctly. Operate the system and verify the concern is still present. Is the concern still present?	Yes	Install a new PCM. See POWERTRAIN CONTROL MODULE (PCM) REMOVAL / INSTALLATION , . Test the system for normal operation.
5		No	The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.
6	CHECK FOR CORRECT INSTRUMENT CLUSTER OPERATION Disconnect all instrument cluster connectors. Check for: corrosion damaged pins pushed-out pins Connect all instrument cluster connectors and make sure they seat correctly. Operate the system and verify the concern is still present. Is the concern still present?	Yes	Install a new instrument cluster. see INSTRUMENT CLUSTER . Test the system for normal operation.
6		No	The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.