Code 51

This DTC does NOT flash the CHECK TRANS indicator and does NOT set the BACKUP MODE.

CIRCUIT DESCRIPTION:
The Engine Coolant Temperature is measured by a sensor in the coolant system. This information is used by the Engine Control Module (ECM) for the engine. The ECM provides the information: Engine Warm to the Transmission Control Module (TCM) when the ECM measures a temperature higher than 70°C (158°F).
- The information is provided using a wire between the ECM terminal A9 and the TCM terminal D14. When the engine is warm the ECM connects its terminal A9 to ground using a Low Side Driver. When the engine is Cold the ECM lets this wire open and the TCM pulls it up to 5 volts.
- When Ignition is ON and Engine is OFF: the ECM always sends the information "engine cold" even if the engine is warm. The information is valid only when the engine is ON.

DIAGNOSTIC AIDS:
- This Diagnostic is not an electrical test done by the TCM but a test between different information ("logic test").
- Detection conditions of engine always cold:
- Engine seen as cold: wire short to voltage or open.
- Transmission Oil Temperature > 100°C (212°F) or more than 20 minutes since last ignition cycle.
- Detection conditions need to be present for at least 6 seconds.
- Detection conditions of engine always warm:
- Engine seen as warm: wire short to ground.
- Transmission Oil Temperature <0°C (32°F).
- Without problem on Transmission Temperature sensor then: voltage on A/T Oil Temperature sensor < 4.74 V.
- Detection conditions need to be present for at least 6 seconds.
- Action after the detection time: No action.
- Recovery conditions: To recover, Engine Coolant Temperature change information need to be present for more than 6 seconds.





- This DTC can be set when there is no problem at all. This is due to the fact that when the engine stalls the ignition is still ON then Engine Control Module (ECM) provides a false information: engine cold. The Transmission Control Module (TCM), knowing that the last ignition cycle happened more than 20 minutes ago, then sets DTC51.
- Using the Scan Tool you can check with TECH1:
F0: ENG. TEMP. SW information. When the engine is cold or when the engine is OFF the TECH1 should show: COLD. When the engine is warm the TECH1 should show WARM.
- This DTC is not very important. In the worst case it would not allow the Torque Converter Clutch (TCC) to be applied. This will cause low fuel economy.