The OBD2 code P00B4: Radiator Coolant Temperature Sensor Circuit High signals an issue where the electrical signal from the radiator coolant temperature sensor to the engine control module (ECM) is higher than expected.
This condition can lead to a variety of symptoms such as hard cold starts, erratic idle, and occasional engine stalling. Properly diagnosing and correcting this issue is vital for ensuring the engine runs smoothly and within its optimal temperature range.
P00B4 quick overview
| Meaning | P00B4: Radiator Coolant Temperature Sensor Circuit High |
| Is it serious? | Yes, it can lead to engine performance problems and should be addressed promptly. |
| Possible causes | – Damaged radiator coolant temperature sensor – Faulty wiring harness or connector pins – Corrosion affecting the sensor’s performance |
| How to diagnose? | Visually inspect the radiator coolant temperature sensor for damage or leakage. Test the sensor’s resistance using a multimeter. Check the wiring harness for wear, corrosion, or damage. Verify proper grounding and continuity within the circuit. |
P00B4 Meaning
When your car’s computer gets a “too hot” signal from the coolant temperature sensor—even when it’s not—the P00B4 code pops up. It’s like getting a fever reading from a thermometer that’s not working right.
This false alarm can make your car act strangely, like struggling to start on a cold morning or idling roughly. Fixing the problem usually involves checking the sensor and its wiring to make sure everything’s in good shape and correctly connected, ensuring the engine gets the right information about its cooling needs.
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How to fix P00B4 – learn from mechanics
I looked into P00B4 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.
Case #1: BMW P00B4
Vehicle Information 2015 BMW 3 Series 328i
Issue + Repair History
- Hard cold starts reported by the owner.
- Engine occasionally stalls during idle.
- No previous repairs mentioned.
Other OBD2 Codes + Test Results
- OBD2 Code: P00B4 (Radiator Coolant Temperature Sensor Circuit High).
- Live data indicates inconsistent temperature readings from the coolant temperature sensor.
- No additional diagnostic trouble codes detected.
Mechanic Suggestions
- Begin by visually inspecting the radiator coolant temperature sensor for any visible signs of damage or leakage.
- Use a multimeter to test the resistance of the sensor and ensure it falls within the specified range according to the manufacturer’s specifications.
- Check the wiring harness connected to the coolant temperature sensor for any signs of wear, corrosion, or damage that could affect the sensor’s performance.
- Verify proper grounding and continuity within the circuit to ensure accurate sensor readings.
Final Fix Upon inspection, it was found that the radiator coolant temperature sensor was experiencing a high electrical value, triggering the P00B4 fault code. The sensor and its wiring harness were examined, revealing a damaged connector pin causing an intermittent high resistance connection. The connector pin was replaced, and the wiring harness was repaired. After the repairs, the coolant temperature sensor provided consistent readings, eliminating the reported hard cold starts and engine stalling issues, effectively resolving the problem.
Case #2: Ford P00B4
Vehicle Information 2012 Ford Focus SE
Issue + Repair History
- Erratic idle reported by the owner.
- No previous repairs mentioned.
Other OBD2 Codes + Test Results
- OBD2 Code: P00B4 (Radiator Coolant Temperature Sensor Circuit High).
- Live data shows fluctuating temperature readings from the coolant temperature sensor.
- No additional diagnostic trouble codes detected.
Mechanic Suggestions
- Inspect the radiator coolant temperature sensor for any visible signs of damage or corrosion.
- Test the resistance of the sensor using a multimeter to ensure it falls within the specified range.
- Check the wiring harness connected to the coolant temperature sensor for any loose or damaged connections.
- Ensure proper grounding and continuity within the circuit to maintain accurate sensor readings.
Final Fix After thorough inspection, it was discovered that the radiator coolant temperature sensor was experiencing a high electrical value, leading to the P00B4 fault code. The sensor showed signs of corrosion, affecting its performance. The sensor was replaced with a new one, and the wiring harness connections were cleaned and secured. Following the replacement and maintenance of the sensor and wiring, the erratic idle issue was resolved, restoring normal engine operation.
Case #3: Toyota P00B4
Vehicle Information 2015 Toyota Camry LE
Issue + Repair History
- Owner reported hard cold starts and erratic engine performance.
- No previous repairs mentioned.
Other OBD2 Codes + Test Results
- OBD2 Code: P00B4 (Radiator Coolant Temperature Sensor Circuit High).
- Live data reveals inconsistent temperature readings from the coolant temperature sensor.
- No other diagnostic trouble codes detected.
Mechanic Suggestions
- Begin by visually inspecting the radiator coolant temperature sensor for any signs of physical damage or corrosion.
- Use a multimeter to test the resistance of the sensor and ensure it falls within the specified range.
- Check the wiring harness connections leading to the coolant temperature sensor for any loose or damaged wires.
- Verify proper grounding and continuity in the circuit to maintain accurate sensor readings.
Final Fix Upon inspection, it was found that the radiator coolant temperature sensor was experiencing a high electrical value, leading to the P00B4 fault code. The sensor showed signs of corrosion and deterioration, affecting its performance. The sensor was replaced with a new one, and the wiring harness connections were cleaned and secured. Following the replacement and maintenance of the sensor and wiring, the hard cold start and erratic engine performance issues were resolved, restoring normal vehicle operation.
How to diagnose P00B4
I made you an overview of solving this DTC, based on all the advice that was suggested by certified mechanics to address this issue in previously mentioned service cases.
| Diagnostic Step | Brief Explanation |
|---|---|
| Inspect the radiator coolant temperature sensor | Looks for any physical damage or signs of corrosion that could impair sensor function. |
| Test the sensor’s resistance | Measures if the sensor operates within the specified range, indicating its health or malfunction. |
| Check the wiring harness | Searches for any electrical issues that could cause the sensor to relay incorrect signals. |
| Verify proper grounding | Ensures the sensor circuit has a solid ground connection, crucial for accurate readings. |
Car Diagnostics Training
- Car Electrical basics
- OBD-II scanner basics
- How to use an OBD reader
- Introduction to a Bi-directional Scan tool
- OBD scanner buyer’s guide + discounts
I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko