Supply to sensors fault. No supply.


Created: 01. 10. 2005
Updated: --. --. ----

Model: 306 N5 with XU10J4R (2.0 litre) engine, AL4 automatic transmission.

Symptoms

Initial checks
In parameters check engine load. If the engine load is at a constant 88% in the foot off position, check the TPS, the connector and the wiring between the ECU and the Throttle Position Switch.

The engine load in the foot off position is 6%, in the full throttle position 88%. If there is no change with throttle movement, check the TPS.

Rectification
The TPS was at fault. Replaced TPS.

General sensor information
The TPS sensor for the automatic transmission is a rheostat type and is housed in the same casing as the TPS for the fuel management system, it is mounted on the lower side of the throttle body. The transmission sensor can be identified by the blue 3-way connector.

Summary for this fault.
In this particular case the problem was caused by a faulty TPS that was giving a permanent full throttle signal. This caused the transmission ECU to cut the supply to the sensors and go into limp-home mode. Diagnosis was somewhat difficult due to the fact that a fault code was generated that pointed in the direction of one of the symptoms and not the cause of the problem. After checking the fluid pressure and temperature sensor wiring and connections many times, it became clear that the transmission control unit was not supplying the current for the sensors. The suspicion turned now towards the ECU which was substituted without success. At this point it became clear that an input parameter had to cause the ECU to shut off the sensor supply. The only irregular known parameter was the engine load at a constant 88%. A quick wiggle on the blue TPS connector proved the theory. Once the throttle signal was back to normal, the ECU restored the power supply to the sensors and the system returned to normal operation.

Some basic testing information.

  1. Resistance across pin 1 and 2, 2kΩ constant.
  2. Resistance across pin 1 and 3, 2.8kΩ when spindle turned clockwise to full stop.
  3. Resistance across pin 1 and 3, 1kΩ when spindle turned counter clockwise to full stop.

When turning the spindle of the throttle position sensor for the automatic transmission the resistance between pin 1 and pin 3 should change gradually in a smooth curve without any high or low resistance spikes.

Throttle Position Sensor


Technical information by
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