DTC 311

FA. DTC 3-1-1
3-1-1 RPM signal absent

Principle of operation

The RPM signal is supplied by a sensor on the transmission, which measures the input speed after the torque converter. The signal is used to compare the transmission speed with the vehicle speed, enabling the gearshifting times to be computed. The engine and vehicle speed signals influence the line pressure, control of the lock-up function and torque reduction, resulting in smooth gearshifting.

Fault description

The TCM does not receive a signal from the RPM sensor although the car is in motion. The MIL on the combined instrument flashes.





Circuit description

The circuit consists of the TCM, RPM sensor and associated wiring and connectors.





1
Measuring resistance of RPM sensor and leads

- Switch off ignition.
- Connect break-out box to wiring (30-pin connector).

Connect ohmmeter between # 16 (NCO) and # 17 (NCOG).

- If instrument indicates 4OO-8OO Ohm, sensor and leads are OK.

In this case, DTC is due to intermittent fault. Check wiring and connections for open-circuit. Check leads and connections as described in Testing and Inspection, General Tests Component Tests and General Diagnostics and return to Testing and Inspection. Diagnostic Procedures

- If instrument indicates other value, proceed to next step.

2
Measuring resistance of RPM sensor

- Switch off ignition.
- Measure at connector D on transmission (sensor side).

Connect ohmmeter between terminal 1 (NCO) and 2 (NCOG).

- If instrument indicates 400-800 Ohm, sensor is OK.

Check leads for short-circuit to ground and check ground terminal connection as described in Testing and Inspection, General Tests Component Tests and General Diagnostics then return to Testing and Inspection. Diagnostic Procedures

- If instrument indicates other value, sensor is faulty. Replace RPM sensor.