The P112F code on GMC vehicles indicates a malfunction of the Radiator Coolant Temperature (RCT) sensor. The ECM compares data from the RCT sensor with that from the Engine Coolant Temperature (ECT) sensor. If the difference exceeds specifications after the engine has been shut down, the code is stored.
Common Symptoms
- Check Engine Light On (P112F code sometimes accompanied by P0116-P0118).
- Radiator Fan Running Continuously.
- Potential Overheating if the cooling system does not regulate correctly.
Main Causes
| Category | Details |
|---|---|
| Faulty RCT Sensor | Internal resistance out of specifications (typically 200–5,000 Ω depending on temperature). |
| Electrical Issues | Cut wiring, short circuit, or corroded connector (5V or ground wires). |
| Faulty ECM | Damaged 5V signal or reference circuit. |
| Coolant Problem | Low level, air bubbles, or stuck thermostat. |
Diagnostic Steps
1. Preliminary Checks
- Coolant Level: Top up if necessary (50% antifreeze mixture).
- Air Bleed: Avoid air bubbles in the circuit (specific GMC procedure).
2. RCT Sensor Test
- Location: On the radiator or lower hose.
- Resistance: Disconnect the connector and measure with a multimeter:
- When Cold (20°C): ~3,500 Ω.
- When Hot (90°C): ~200 Ω.
- ECT/RCT Comparison: Use a scan tool to check temperature consistency (max. 10°C difference after engine shutdown).
3. Electrical Inspection
- 5V Power Supply: Measure voltage between the signal wire and ground (engine off).
- Continuity: Check wires between the sensor and ECM (no short circuit or break).
4. Thermostat Test
- Operation: Check for progressive opening starting at 90°C (marker on the thermostat).
- Replacement: If stuck open/closed (cost: €30–100).
Solutions and Costs
| Problem | Solution | Cost (€) |
|---|---|---|
| Faulty RCT Sensor | Replace with an OEM part (e.g., ACDelco 213-4484). | 50–120 |
| Damaged Wiring | Repair the harness or replace the connector. | 30–150 |
| Faulty ECM | Reprogramming or replacement (at a dealership). | 500–1,200 |
Best Practices
- Use Dex-Cool coolant (specific to GMC) to avoid corrosion.
- Reset the ECM after repair to clear adaptations.
FAQ
Q: Can I drive with a P112F code?
A: Yes, but monitor the temperature. Overheating can damage the engine.
Q: Why does the code return after replacing the sensor?
A: Check the wiring or thermostat. A clogged circuit or ECM fault may persist.