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Detroit Fault Codes SPN 84/FMI 20 – EPA07 – GHG14

08/12/2025
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SPN 84/FMI 20 - EPA07 - GHG14
Vehicle Speed Sensor Erratic
SPN 84/FMI 20
Description Vehicle Speed Sensor Erratic
Monitored Parameter Vehicle Speed Sensor (VSS)
Typical Enabling Conditions RPM greater than 1500, Torque Demand On
Monitor Sequence None
Execution Frequency Continuous when enabling conditions met
Typical Duration 10 Seconds
Dash Lamps MIL
Verification RPM greater than 1500, Torque Demand On

Check as follows:

1. Are there any battery (SPN 168/FMI any) or Controller Area Network (CAN) (SPN 625/FMI any) faults present?

1.1. Yes; repair those faults first.

1.2. No; Go to step 2.

2. Has the Common Powertrain Controller (CPC) been recently reprogrammed?

2.1. Yes; insure the VSS parameters are configured correctly for the vehicle application. If OK, Go to step 3.

2.2. No; Go to step 3.

3. Is the VSS hardwired or transmitted via J1939?

3.1. Hardwired; Go to step 4.

3.2. J1939; refer to the A&I manual for the correct parameter configuration. If configuration is correct, refer to the Original Equipment Manufacturer (OEM) material for J1939 troubleshooting.

4. Disconnect the VSS harness connector; refer to OEM literature for location.

5. Inspect the VSS harness connector for bent, spread, or corroded pins.

5.1. If pin damage is found, repair as necessary.

5.2. If no pin damage is found, Go to step 6.

6. Disconnect CPC connector #3.

7. Measure the resistance between CPC connector #3 pins 13 and 14.

7.1. If the resistance is less than 1K ohms, repair the short between CPC connector #3 pins 13 and 14 and the VSS connector.

7.2. If the resistance is greater than 1K ohms, Go to step 8.

8. Measure the resistance between CPC connector #3 pin 13 and the VSS+ harness connector.

8.1. If the resistance is less than 1K ohms, repair the wire between CPC connector #3 pin 13 and the VSS+ harness connection.

8.2. If the resistance is greater than 1K ohms, Go to step 9.

9. Measure the resistance between CPC connector #3 pin 14 and the VSS- harness connector.

9.1. If resistance is greater than 10 ohms, repair the wire between CPC connector #3 pin 14 and the VSS- harness connection.

9.2. If the resistance is greater than 1K ohms, refer to OEM literature for VSS sensor diagnostics.

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