P0712

What it means

P0712 means the transmission control module has seen the signal from transmission fluid temperature sensor A fall below the expected range. This usually means the signal voltage is too low, which the module reads as an implausibly high fluid temperature, often because of a short to earth in the circuit or a faulty sensor. The module may then use a default temperature value and change how the gearbox behaves.

Symptoms

• Gearbox warning light or malfunction indicator lamp on
• Harsh, delayed or erratic gear changes
• Gearbox stuck in a fixed gear or limp mode
• Torque converter lock-up not engaging or being inhibited
• Poor fuel economy
• Temperature readout in live data showing an implausibly high or fixed value

Possible causes

• Faulty transmission fluid temperature sensor with internal shortlikely
• Wiring chafed or shorted to earth in the sensor signal circuitlikely
• Water, fluid or contamination in the connector or internal gearbox harness causing a shortpossible
• Damaged internal gearbox wiring loom or valve body connector (on units where the sensor is built in)possible
• Fluid genuinely overheating due to a fault such as a slipping clutch or cooler restrictionpossible
• Faulty transmission control modulerare

How to diagnose

1. Read all stored and pending codes and note the freeze frame data, including fluid temperature and vehicle speed at the time of setting.
2. Check the gearbox fluid level and condition against the manufacturer's procedure, looking for burnt smell, debris or contamination.
3. Inspect the sensor connector and harness for damage, chafing, corrosion, moisture and fluid ingress.
4. With the gearbox cold, compare the live fluid temperature reading with ambient temperature; a very high reading on a cold gearbox points to a short or sensor fault.
5. Unplug the sensor and see whether the reading changes to an open-circuit value; if it does, the sensor or its connection is suspect, if not, suspect a short in the wiring.
6. Test the signal wire for a short to earth and check the reference and return circuits using the wiring diagram for that model.
7. Measure the sensor resistance and compare it with the manufacturer's temperature specification, as the sensor location and access vary by model and gearbox.
8. Check the cooler flow and look for signs of overheating if the live data shows the temperature really is high.

How to fix

• Replace the fluid temperature sensor, or the part of the assembly that contains it, if it fails resistance or signal checks.
• Repair or replace the damaged wiring or connector terminals, and seal against moisture ingress.
• Replace the internal gearbox harness or valve body connector where it is found to be shorted.
• Correct the cause of any genuine overheating, such as a restricted cooler or low or degraded fluid, and refill to the correct specification.
• Replace or repair the transmission control module only after wiring and sensor faults have been ruled out.

Can I keep driving?

Nearby codes

• P0711GenericTransmission Fluid Temperature Sensor A Circuit Range/Performance
• P0713GenericTransmission Fluid Temperature Sensor A Circuit High