How is fault code P0115 fixed?

A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training. 1. Plug in a scan tool and look at the live coolant temp value with the engine dead cold. If it reads -40C or +130C with a stone-cold engine, the sensor or its circuit is reporting nonsense and that's your direction 2. Unplug the connector and have a proper look. Green crusty pins, coolant inside the plug, or a wire pulled out of the back are all common and cost nothing to find 3. Back-probe the sensor connector with a multimeter, ignition on, and check for the 5V reference. No reference voltage points at wiring or ECU, not the sensor 4. Measure the sensor's resistance across the temperature range and compare to the figures in the manual. A cold sensor should read a few thousand ohms, dropping to a couple of hundred when hot. Way out, or reading open, means a new sensor 5. Check the coolant level and bleed the system if it's low or aerated, since a sensor tip sitting in air gives rubbish readings 6. Compare the coolant temp reading against the intake air temp sensor first thing on a cold m

Engine Coolant Temperature Circuit Malfunction

Jump to the fix

Severity

Medium

Can I keep driving?

Usually drivable, but get it diagnosed without delay.

First step

A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training. 1. Plug in a scan tool and look at the live coolant temp value with the engine dead cold. If it reads -40C or +130C with a stone-cold engine, the sensor or its circuit is reporting nonsense and that's your direction 2. Unplug the connector and have a proper look.

PPowertrain
0Generic code
1Fuel / Air
15Sequence number

What does it mean?

OBD II fault code P0115 is defined as “Engine Coolant Temperature Circuit Malfunction”, and is set when the PCM (Powertrain Control Module) detects a circuit voltage value in the engine coolant temperature sensor that falls outside of a predetermined range. On most applications, a code will be stored and a warning light illuminated when the PCM detects a voltage/resistance value that deviates to either side from design parameters by about 10%, and/or for a specified time.

Note that both the degree of deviation from specified electrical values and the time required before a code sets can vary between applications. Consult the repair manual for the application being worked on for the exact code setting parameters. Temperature sensors on modern engines are of the variable resistance type that converts temperature into signal voltages.

In general, the cooler the engine coolant, the higher the resistance but as the engine coolant temperature increases, resistance drops, thereby increasing the signal voltage to the PCM. Note that it is rare for an engine to have only one engine coolant temperature sensor. Most applications use one sensor to control the heat gauge, and another that communicates with the PCM to control the electric radiator fan, and/or cold start valves on some older applications.

Some diesel engines may have a dedicated coolant temperature sensor to control the working of the glow plugs. The image below shows a typical engine coolant temperature sensor location. Note that actual designs and locations differ widely between applications.

Symptoms

Likely causes

How to fix it

Codes From the Same System

All Fault Codes

Related Similar Codes

This information follows the generic OBD-II definition and does not replace a vehicle-specific diagnosis. The severity rating is rule-based; an authorised diagnostic reading is required for a definitive answer.