P0118 Fault Code: ECT Sensor Circuit High Input

Code: P0118
System: Cooling system
Severity: Warning

In short

P0118 = ECT Sensor Circuit High Input. The code belongs to the engine and transmission group.
CarCoding classifies this code as warning severity under cooling system.
The database lists 4 possible causes; freeze frame and live data decide which one applies — work by measuring, not by replacing parts.

What does P0118 mean?

The control unit stores a standard fault code when a measurement falls outside its expected range. P0118 corresponds to ECT Sensor Circuit High Input.

The leading P tells you which system group the code belongs to: Powertrain — engine and transmission. A 0 in the second position means the code is standardised by SAE/ISO, so it carries the same meaning across manufacturers. CarCoding files this code under Cooling system.

A fault code is not the name of a broken part. It tells you what the control unit saw; which part caused it is decided by measurement and elimination. That is why the list of causes below is not a shopping list but a list of things to check.

For the control unit, coolant temperature is not a single value but a time-temperature curve; codes in this group arise when the temperature does not follow the expected curve. All fault codes in the Cooling System group →

Possible causes

Possible causes the CarCoding database holds for P0118:

ECT sensor open circuit
Broken wire
Connector corrosion
Faulty sensor

The order is not a probability ranking or a diagnostic sequence. The same code can have different causes on different vehicles, so treat the list as a starting set to be narrowed down by measurement.

How is it diagnosed?

The sequence below is not specific to P0118; it applies to OBD-II fault code diagnosis in general. These are the steps that are most often skipped:

Read all the codes together. A single code is rarely the whole story; the other codes stored at the same time often point to the real cause.
Read the freeze frame. The rpm, engine load, coolant temperature and speed at the moment the code was stored tell you under what conditions the fault occurred. It is the single most valuable piece of data you have.
Identify which list the code is in. Confirmed (Mode 03), pending (Mode 07) and permanent (Mode 0A) codes are not the same thing. A code that appears only in the pending list means the fault has not been confirmed yet — most likely it is intermittent.
Look at live data. Deliberately recreate the condition from the freeze frame and watch the relevant sensor values in real time. If you can reproduce the fault, you no longer have to guess.
Clear and verify. After fixing the fault, clear the code (Mode 04), take a verification drive similar to the freeze frame conditions and read the pending codes again. An empty list means the fault is really gone.

The cost of clearing codes: Clearing also resets the emissions readiness monitors. Until those monitors return to “complete”, the vehicle may not pass an emissions test. So read and record the codes before clearing them.

Can you keep driving?

CarCoding classifies P0118 as warning severity: it is not in the group that requires stopping immediately, but the fault will not clear itself. If you notice changed driving behaviour, loss of power, higher consumption or unusual noise, bring the diagnosis forward.

A stored code can also affect the emissions readiness monitors and the outcome of a roadworthiness test. How your vehicle behaves right now matters more than this general classification: if there is a red warning on the dashboard, do not keep driving.

Related fault codes

Other fault codes in the same system (cooling system):

See all fault codes →

Read P0118 on your own vehicle

With an ELM327-based BLE OBD2 adapter, CarCoding reads confirmed, pending and permanent fault codes separately, pulls the freeze frame and explains every code in plain language. Clearing codes is done from the app as well. The app is free to download.

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Frequently asked questions

What does fault code P0118 mean?

P0118 is an OBD-II fault code meaning “ECT Sensor Circuit High Input”. In the CarCoding database it sits in the Cooling system group with warning severity. The code does not say which part is broken; it says which measurement the control unit found outside its expected range.

What are the possible causes of P0118?

The CarCoding database lists the following possible causes for P0118: ECT sensor open circuit; Broken wire; Connector corrosion; Faulty sensor. This list is not a diagnostic order; measurement decides which one applies.

Can you drive with fault code P0118?

P0118 is in the warning severity class: it is not in the group that requires stopping immediately, but the fault will not clear itself. If you notice changed driving behaviour, loss of power or higher consumption, bring the diagnosis forward. Base the decision on how the vehicle behaves right now and on the freeze frame data.

Will clearing P0118 fix it?

Clearing a code (OBD-II Mode 04) only resets the record in the control unit and the warning lamp; if the fault is still present the code returns once the verification cycle completes. Clearing also resets the emissions readiness monitors, so clearing codes before an emissions test can cause the vehicle to fail. The right order is: record the code and the freeze frame, fix the fault, clear the code, take a verification drive and read the pending codes again.

Data source: the CarCoding fault code database. Code definitions follow the SAE J2012 standard; manufacturers may use different wording for their own codes. Everything on this page is generated from the code-specific database records.

Disclaimer: This page offers general diagnostic guidance and does not replace an inspection by a qualified workshop. Any work carried out on the vehicle is your own responsibility.