How to Solve Caterpillar C9 Engine Vehicle Speed Loss of Signal Error?

This instruction show you guide on how to solve Caterpillar C9 engine 31 84-1 fault code vehicle speed loss of signal error.

 

The Engine Control Module (ECM) detects the following condition:

The “VSL Protection” is not programmed to “TEL”.

The ECM does not detect vehicle speed when conditions indicate that vehicle speed should be present.

Desired engine speed is greater than the programmed “VSL Protection”.

 

What you need?

CAT ET 2026A

Cat adapter 3 

 

 

For these vehicles, the vehicle speed signal is provided by an electronic source.The signal is received over a single wire that is connected to ECM vehicle harness connector J1/P1-32 (vehicle speed in positive).Do not make any other connection to this line. A speedometer is an example of a connection that should not be made to this line.For this type of signal the ECM vehicle harness connector J1/P1- 33 vehicle sped in negative) must not be connected to the ECM in order to prevent introducing electrical noise into the circuit.

 

For vehicle speed problems on trucks that are equipped with either of these vehicle speed sources,first inspect the wiring from the electronic source to the engine ECM for open circuits or for short circuits.

 

The ECM can be configured to receive vehicle speed information from an electronic transmission control unit via the J1939 data link.The transmission must be capable of supporting the “1939 ETC1 Broadcast Message (PGN 61.442 Bytes 2 & 3)”.

 

This message provides the speed of the transmission output shaft. This feature requires the hardware for the J1939 data link to be installed in the chassis of the vehicle. This also requires a transmission that is electronically controlled and capable of supporting the necessary J1939 protocol.

 

When the engine is configured for the J1939 option, the circuit for the ECM vehicle speed input (terminals 32 and 33) will be ignored.The ECM uses the “Vehicle Speed Cal (1939-Trans)” parameter value in order to calculate vehicle speed. The ECM uses the parameter value and the speed of the output shaft that is received over the J1939 data link to calculate the vehicle speed.

The “Vehicle Speed Cal (1939-Trans)” parameter is based on the revolutions per mile of the output shaft.There are several methods that can be used to arrive at this calibration value. Refer to Troubleshooting.,”Vehicle Speed Circuit – Calibrate” for details.

 

The ECM can be configured to receive vehicle speed information from the Anti-lock Brake System (ABS) via the J1939 data link.The ABS must be capable of supporting the “1939 High Resolution Wheel Speed Broadcast Message (PGN 65, 134 Byte 5-8), which provides wheel speed from the two rear wheels. The ABS will broadcast the assumed tire revolutions per mile.

 

Regardless of the source that is used to determine vehicle speed. the ECM uses the calculated value for the vehicle speed in the same manner to control several features and functions.The diagnostics for vehicle speed function similarly when either a hard-wired signal is provided to the ECM from a speed sensor, or a message is sent to the ECM via the J1939 data link.If the ECM detects a loss of vehicle speed or a value that is invalid. a fault code will be logged in order to alert the operator or the technician of the presence of a problem.

 

Probable Causes:

1 ECM Connection

2 Speed not calibrated properly in ECM

3 Vehicle Speed Sensor

4 Vehicle Speed Sensor connection/harness

5 Failed ECM