P0118 on a BMW: Causes, Fixes & Repair Cost
🟠 Moderate severity · drivable
Safe to drive, but the engine may run rich and the aux fan may act up until the sensor circuit is repaired.
What P0118 means on a BMW
On a BMW, P0118 means a coolant temperature sensor is sending a high-voltage signal that the computer reads as the engine being very cold. Many BMW engines use coolant temperature sensors in the cylinder head and at the radiator outlet, so an open circuit in either sensor or its wiring can set this code. The computer then enriches the fuel mixture as if the engine were cold.
Is P0118 common on BMWs?
P0118 appears on 3 Series, 5 Series, X3, and X5 models with age. BMW engine wiring can become brittle after years of heat, and sensor failures are known on the N-series engines found in many of these models.
Commonly reported on: 3 Series, 5 Series, X3, X5.
Symptoms
- Check engine light on
- Poor fuel economy
- Hard cold start
- Cooling fan running at odd times
Common causes
- most common: Faulty coolant temperature sensor
- common: Open sensor wiring
- common: Brittle or chafed wiring harness
- less common: Corroded or loose connector
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Replace the coolant temperature sensor | Yes | $30–90 |
| Repair the sensor wiring | Mechanic | $100–250 |
| Have a shop diagnose the circuit | Mechanic | $120–180 |
Frequently asked questions
Other common BMW codes
P0118 on other brands
Looking for the full (non-brand-specific) guide? See the P0118 code page →
Browse all BMW codes: BMW hub →
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.