What is OBD-II Code P00B4 – Radiator Coolant Temperature Sensor Circuit High

The OBD-II system is an onboard diagnostics system in vehicles that monitors and detects potential issues. If a problem is detected, it will set a diagnostic trouble code (DTC) and turn on the check engine light. One of the codes that OBD-II can set is P00B4, which indicates an issue with the Radiator Coolant Temperature Sensor Circuit High. In this article, we will explain the meaning of P00B4 and how to fix it.

What is OBD-II Code P00B4?

P00B4 is a generic code that is set when the Radiator Coolant Temperature Sensor Circuit High is detected. The Radiator Coolant Temperature Sensor measures the temperature of the engine coolant and relays that information to the engine control module (ECM) or powertrain control module (PCM). The ECM/PCM uses the information to adjust fuel injection and ignition timing, among other things.

When the ECM/PCM detects that the signal from the Radiator Coolant Temperature Sensor is too high, it will set the P00B4 code. There are several potential reasons why this may occur, including a faulty sensor, damaged wiring, or an issue with the ECM/PCM.

Symptoms of OBD-II Code P00B4

When P00B4 is set, the check engine light will come on. In some cases, the vehicle may experience other symptoms, such as:

– Decreased fuel efficiency
– Engine overheating or running hot
– Rough idle or stalling

If you notice any of these symptoms or the check engine light is on, it’s best to have your vehicle inspected by a qualified mechanic.

How to Fix OBD-II Code P00B4

To fix P00B4, the first step is to diagnose the root cause of the problem. This can be done using a scan tool to read the DTC and determine the exact cause. Here are some of the potential solutions:

1. Replace the Radiator Coolant Temperature Sensor

If the sensor is faulty, it will need to be replaced. This is a relatively simple and affordable fix that can be done by a qualified mechanic or DIYer with some basic automotive knowledge.

2. Check for Damaged Wiring

Corrosion or damage to the wiring leading to the sensor can cause the signal to become corrupted. A mechanic will need to inspect the wiring harness and look for any signs of damage or wear. If necessary, the wiring will need to be replaced or repaired.

3. Check the ECM/PCM

If both the sensor and wiring are in good condition, the issue may be with the ECM/PCM itself. In this case, the ECM/PCM will need to be diagnosed by a qualified mechanic and potentially replaced.

It’s important to fix P00B4 as soon as possible to prevent potential damage to the engine and ensure the vehicle is running smoothly.

Frequently Asked Questions

1. Can P00B4 cause engine damage?
While P00B4 itself is not likely to cause engine damage, it can lead to issues such as overheating, which can damage the engine if left untreated.

2. Can I still drive my vehicle with P00B4?
While it’s technically possible to drive with P00B4, it’s not recommended. The issue can cause decreased fuel efficiency and other problems that can make the vehicle unsafe to drive.

3. Can I fix P00B4 myself?
If you have automotive experience and the necessary tools, it’s possible to fix P00B4 yourself. However, it’s best to leave the repairs to a qualified mechanic if you’re unsure about what you’re doing.

4. How much does it cost to fix P00B4?
The cost of fixing P00B4 will depend on what is causing the issue. Replacing the sensor is typically the most affordable option, while ECM/PCM replacement is more expensive.

5. Can P00B4 be prevented?
Proper maintenance, including regular coolant flushes, can help prevent issues with the Radiator Coolant Temperature Sensor and potentially prevent P00B4. It’s also important to address any check engine lights or other symptoms as soon as they arise.


P00B4 is a generic OBD-II code that indicates an issue with the Radiator Coolant Temperature Sensor Circuit High. This can cause symptoms such as decreased fuel efficiency, overheating, and rough idle. If you experience any of these symptoms or the check engine light comes on, it’s best to have your vehicle inspected by a qualified mechanic. The issue can be fixed by replacing the sensor, checking for damaged wiring, or diagnosing potential issues with the ECM/PCM. Proper maintenance can help prevent P00B4 and other potential issues.

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