Odometer Accuracy - keywords IPC speedometer
| Subject: | Odometer Accuracy |
| Models: | 1995-2009 All GM Passenger Cars and Light Duty Trucks |
This PI was superseded to update model years. Please discard PIC3100A.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:
A customer may comment that their vehicle's odometer appears to be inaccurate relative to a known distance traveled. This known distance traveled is probably based on odometer readings from other vehicles the customer has driven.
Recommendation/Instructions:
Even though there is not a federal regulation pertaining to odometer accuracy, some states do have specific laws. Generally, a tolerance of plus or minus 4% is allowed, however, it is the responsibility of each dealer to be familiar with local requirements before attempting to verify the accuracy of a customer's odometer.
To verify the accuracy of the odometer, the dealer should obtain a hand-held GPS unit to test the odometer. While driving on a straight road, over a mile long, mark the waypoint on the GPS when the odometer (not the trip odometer) rolls over a digit. When it rolls to the next digit, take a reading and compare the two for actual distance traveled versus the odometer reading.
If a hand held GPS unit is not available, the only other option is to verify the miles traveled using a surveyor's wheel or a dynamometer. Do not compare with another vehicle. Do not compare with the trip odometer. Also, mileage markers on an expressway are typically not accurate enough to perform exact measurements.
Additionally, dealers should confirm that the original size tires and wheels are mounted on the vehicle and that the axle ratio is as specified per the SPID label and have not been modified. Dealers should insure that the vehicle calibration is for that tire size and axle ratio when applicable. If correct and the odometer is beyond the required limit, consideration should be given to the relationship between the VSS and the reluctor on the transmission output shaft. Close inspection should be made of the associated wiring and any connectors in the circuits. Finally, it may be necessary to exchange the IPC with a replacement unit.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
