Pinpoint Test AC: Incorrect Speedometer Indication
Instrumentation, Message Center and Warning Chimes
Pinpoint Tests
Pinpoint Test AC: Incorrect Speedometer Indication
Normal Operation
The PCM calculates vehicle speed from the transmission Output Shaft Speed (OSS) sensor input and from the tire size and axle ratio configuration in the Vehicle Identification (VID) block of the PCM. The PCM provides the Instrument Cluster (IC) with the Vehicle Speed Sensor (VSS) signal over the High Speed Controller Area Network (HS-CAN) communication bus. The IC monitors the VSS input from the PCM and commands the speedometer with a corresponding movement of the pointer. Factors that could potentially affect the accuracy of the speedometer are configurable items such as tire size and axle ratio.
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.
This pinpoint test is intended to diagnose the following:
- Tire size configuration
- Axle ratio configuration
- PCM concern
- IC
PINPOINT TEST AC: INCORRECT SPEEDOMETER INDICATION
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AC1 CHECK THE TIRE SIZE CONFIGURATION
- Enter the following diagnostic mode on the scan tool: Module Programming .
- NOTE: The correct tire size can be found on the vehicle certification label on the LH B-pillar. Refer to Identification Codes Application and ID.
- Select programmable parameters and verify that the vehicle has the correct tire size according to the certification label and the tire size is correctly configured in the PCM.
- Is the tire size correct and is the tire size parameter correctly configured?
Yes
GO to AC2.
No
CONFIGURE the tire size. TEST the system for normal operation.
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AC2 CHECK THE AXLE RATIO CONFIGURATION
- Enter the following diagnostic mode on the scan tool: Module Programming .
- Select programmable parameters and verify that the axle ratio is correctly configured in the PCM.
- Is the axle ratio parameter correctly configured?
Yes
GO to AC3.
No
CONFIGURE the axle ratio. TEST the system for normal operation.
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AC3 RETRIEVE THE RECORDED DTCs FROM THE PCM KOEO SELF-TEST
- Check the recorded PCM DTCs from the Key ON Engine OFF (KOEO) self-test.
- Are any DTCs recorded?
Yes
REFER to Computers and Control Systems.
No
GO to AC4.
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AC4 RETRIEVE THE RECORDED DTCs FROM THE IC SELF-TEST
- Check for recorded DTCs from the IC self-test.
- Are any DTCs recorded?
Yes
For DTC U1900, REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test.
If DTC U1900 is still present, REFER to Module Communications Network Testing and Inspection.
For DTC U2023, RETRIEVE and REPAIR all non-network DTCs in the PCM and other modules on the network. REFER to Computers and Control Systems.
For all other DTCs, REFER to DTC Charts. Instrumentation, Message Center, and Warning Chimes
No
GO to AC5.
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AC5 OBSERVE THE SPEEDOMETER OPERATION
- Ignition ON.
- Observe the speedometer while driving the vehicle at various speeds and stopping frequently.
- Does the speedometer begin at 0 km/h (0 mph), indicate the different vehicle speeds and fully return to the 0 km/h (0 mph) position when the vehicle is stopped?
Yes
GO to AC6.
No
INSTALL a new IC. REFER to Instrument Cluster (IC) Instrument Cluster (IC). TEST the system for normal operation.
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AC6 CARRY OUT THE SPEEDOMETER ACTIVE COMMAND USING THE SCAN TOOL
- Ignition ON.
- Enter the following diagnostic mode on the scan tool: IC DataLogger .
- Select the speedometer (SPDOMETER) active command and command the speedometer in increments of approximately 10%. Observe the speedometer. The speedometer starts at 0 km/h (0 mph) and moves approximately 19 km/h (12 mph) for each 10% increment.
- Does the speedometer begin at 0 km/h (0 mph) and move by approximately 19 km/h (12 mph) for each 10% increment?
Yes
GO to AC7.
No
INSTALL a new IC. REFER to Instrument Cluster (IC) Instrument Cluster (IC). TEST the system for normal operation.
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AC7 CHECK THE IC VSS INPUT
- Ignition ON.
- Enter the Instrument Cluster (IC) Dealer Test Mode.
- NOTE: The display below uses xxx's to represent a numeric or alpha-numeric value. The value may display the same amount of characters represented by the xxx's or there may be more/less depending on the type of display. For example: E xxx.x (base cluster) or xxx.x MPH (message center cluster) may display E 25 (base cluster) or 25 MPH (message center cluster). Note that there were 3 x's in the display description but only 2 digits in the actual display.
- Scroll through the displays to E xxx.x (base cluster) or xxx.x MPH (message center cluster).
- Monitor the speedometer and the vehicle speed input at various vehicle speeds.
- Does the speedometer approximately match the vehicle speed input?
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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