C15 – 0084-01 Vehicle Speed loss of signal (31)

Conditions Which Generate This Code:

The ECM detects the following conditions:
• The vehicle speed signal indicates that the vehicle speed is 0 MPH.
• Engine speed is greater than the programmed “VSL Protection” minus 100 RPM for at least 0.06 seconds.
• Desired engine speed is greater than the programmed “VSL Protection”.
• The change in engine speed is less than 133 RPM per second for at least 0.06 seconds.
• The “VSL Protection” parameter is programmed to a value that is less than 2120 rpm.

The following condition must also be met if the “Vehicle Speed Input” is programmed to “J1939-ABS” or “J1939-Trans”.
• The message for vehicle speed is not received over the J1939 data link for more than 0.5 seconds.

System Response:
The ECM will limit engine rpm to the programmed “VSL Protection”. If the ECM is providing the
speedometer signal, the speedometer will show 0 rpm. “DIAG” will be displayed next to the status for
“Vehicle Speed” on the electronic service tool.

Possible Performance Effect:
The ECM will limit engine rpm to the programmed “VSL Protection”.

Note: A fuel system restriction has been known to cause this diagnostic code although this occurrence
is not common. This situation exists because the injectors are unable to provide sufficient fuel in
order to achieve the desired rpm under normal load conditions. Because the ECM cannot reach the desired rpm under the normal load conditions, the ECM suspects that the vehicle is under load. This
should only occur when the vehicle is in motion.

Troubleshooting:
Check the fuel pressure in order to ensure that a fuel system restriction is not the cause of the
problem when the vehicle is not moving.
Perform the following diagnostic procedure: “Vehicle Speed and Speedometer Circuit – Test”

Results:
• OK – STOP.

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