P0118 : Understanding the P0118 Engine Coolant Temperature Circuit High

If you’ve ever found yourself puzzled by the code P0118 flashing on your vehicle’s dashboard, you’re not alone. The world of automotive diagnostics can be complex, but it’s not unchartered territory.

Let’s venture into the realms of understanding what exactly a P0118 Engine Coolant Temperature Circuit High error means.

What is the P0118 Engine Coolant Temperature Circuit High?

Essentially, this code indicates that the Engine Control Module (ECM) has detected an unusually high voltage input from the engine coolant temperature (ECT) sensor. But before we dive deeper, let’s understand how the coolant temperature sensor works.

How the Coolant Temperature Sensor Works

The coolant temperature sensor, typically a two-wire sensor, is a key player in managing your vehicle’s engine performance and emissions. By relaying the coolant temperature to the ECM, it helps optimize fuel injection, ignition timing, and transmission shifting. Quite the multitasker, isn’t it?

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Common Causes of P0118

The P0118 error can primarily result from a handful of causes. Let’s delve into each one.

Faulty Coolant Temperature Sensor

A common offender is a faulty coolant temperature sensor. Over time, these sensors may fail or provide inaccurate readings.

Damaged Wiring or Connector

Wiring issues such as short circuits, open circuits, or bad connectors can disrupt the communication between the ECT sensor and the ECM, leading to the P0118 code.

PCM/ECM Issues

Though rare, issues with the Powertrain Control Module (PCM) or ECM itself can also cause this error.

Symptoms of P0118

Knowing the symptoms associated with P0118 can help you detect the issue early. Here are the most common ones.

Engine Overheating

A faulty ECT sensor might fail to detect and report engine overheating, potentially leading to serious engine damage.

Poor Fuel Economy

If the ECT sensor reads a lower temperature than actual, the ECM may enrich the fuel mixture unnecessarily, causing poor fuel economy.

Irregular Temperature Readings

Fluctuating temperature gauge readings could also indicate a problem with the ECT sensor.

How to Diagnose and Fix the P0118 Code

Fixing the P0118 code involves a series of steps. Let’s break them down.

Inspection Process

Start by inspecting the ECT sensor and its wiring. Look for signs of damage or corrosion.

Replacing the Sensor

If the sensor itself is faulty, it needs to be replaced. This typically involves draining some coolant, removing the old sensor, installing a new one, and refilling the coolant.

Repairing or Replacing Damaged Wiring

If the wiring or connector is damaged, repairing or replacing it will often resolve the problem. However, this can be a complex task and might require professional assistance.

Consulting a Professional

If the error persists despite the above steps, it’s time to seek help from a professional mechanic. In rare cases, issues with the PCM/ECM might be the underlying cause, which should be addressed by a professional.


A P0118 Engine Coolant Temperature Circuit High error is not something to ignore. By understanding its causes, symptoms, and fixes, you can ensure your vehicle remains in top shape. Remember, when it comes to vehicle maintenance, an ounce of prevention is worth a pound of cure.


1. Can I drive my car with a P0118 code?

While you might be able to drive with a P0118 code, it’s not recommended. The faulty readings could lead to engine overheating and severe damage.

2. How much does it cost to fix the P0118 code?

The cost to fix a P0118 code can vary widely based on the underlying issue. Replacing a faulty coolant temperature sensor can be relatively inexpensive, but if the problem lies with the PCM/ECM, costs can escalate.

3. How can I prevent the P0118 code from appearing?

Regular vehicle maintenance, including periodic inspection of the coolant temperature sensor and its wiring, can help prevent this error code.

4. Can a bad thermostat cause a P0118 code?

While a bad thermostat can cause overheating issues, it typically doesn’t cause a P0118 code. This code specifically relates to issues with the ECT sensor or its circuit.

5. Will the check engine light clear itself after replacing the sensor?

The check engine light might not clear itself immediately after replacing the sensor. You may need to use an OBD-II scanner to reset it, or it may clear after multiple driving cycles.

The P0118 code can sometimes be associated with other trouble codes. Here are five codes that could be directly related or might cause a P0118 code:

  1. P0117 Engine Coolant Temperature Circuit Low Input: This code indicates that the Engine Control Module (ECM) has detected an unusually low voltage from the engine coolant temperature (ECT) sensor, which is typically the result of a short circuit.
  2. P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control: If the engine isn’t reaching the necessary temperature to go into closed-loop operation, it could be due to an issue with the ECT sensor, potentially triggering a P0118.
  3. P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature): This code means the engine’s coolant isn’t getting warm enough, fast enough. In some cases, a faulty ECT sensor might cause incorrect readings that trigger this code.
  4. P0217 Engine Overtemperature Condition: This code indicates that the engine is running too hot, which can sometimes be due to a faulty ECT sensor providing incorrect coolant temperature information.
  5. P0480 Cooling Fan I Control Circuit Malfunction: This code is related to the electric cooling fan, which helps to keep the engine cool. A faulty ECT sensor could result in the fan not being activated when needed, potentially leading to engine overheating and the P0480 code.

While these codes may be associated with P0118, it’s important to diagnose each code individually to identify and address the underlying issues correctly.