Radiator Coolant Temperature Sensor Circuit High
The P00B4 code indicates that the Engine Control Module (ECM) has detected a high voltage signal from the radiator coolant temperature sensor circuit. This sensor monitors the temperature of the coolant exiting the radiator. A high voltage reading typically means the sensor is reporting an extremely low temperature (e.g., -40°F) or there is a short to voltage in the wiring. This can cause the ECM to misinterpret coolant temperature, leading to improper fuel mixture, cooling fan operation, and potential engine overheating.
1. Most Common Causes
- Faulty radiator coolant temperature sensor
- Short to voltage in the sensor circuit wiring
- Open circuit or high resistance in the sensor ground
- Corroded or damaged connector at the sensor
- Faulty ECM (rare)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine may run rich or lean
- Cooling fan may run continuously or not at all
- Poor fuel economy
- Possible overheating or failure to reach operating temperature
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Visually inspect the radiator coolant temperature sensor connector and wiring for damage, corrosion, or shorts.
Step 3: Disconnect the sensor and measure resistance; compare to specifications (typically high resistance when cold, low when hot).
Step 4: Check voltage at the sensor connector with key on; should be around 5V reference. If voltage is higher than 5V, suspect a short to battery voltage.
Step 5: If sensor and wiring are okay, test the ECM by checking continuity and signal ground.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. The incorrect temperature reading can cause the engine to run poorly, overheat, or damage the catalytic converter. Have it diagnosed promptly.
How much does it cost to fix?▼
Typically $50-$150 for a new sensor and labor. If wiring repair is needed, costs may be higher.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.