Engine Coolant Temperature Sensor 1 Low Voltage
The coolant temperature sensor voltage is too low.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The engine's computer is getting a signal from the coolant temperature sensor that's lower than expected, which usually means there's an issue with the sensor or its circuit.
What the computer is actually seeing
The engine control module (ECM) expects the coolant temperature sensor to send a voltage signal between 0.5V (cold) to 4.5V (hot). When it sees a voltage below 0.5V, it triggers this fault code.
What a healthy reading looks like
Coolant temperature sensor should read approximately 0.5V (around -40°F or -40°C) to 4.5V (around 266°F or 130°C).
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Inspect the coolant temperature sensor wiring for damage or shorts. - Decision point: If damaged, repair or replace. If ok, proceed.
- 22. Check the connector at the sensor for corrosion or loose connections. - Decision point: If corroded, clean or replace connector and retest. If ok, proceed.
- 33. Measure the voltage at the sensor harness with the engine running. - Decision point: If voltage is below 0.5V, replace the coolant temperature sensor. If voltage is normal, proceed.
- 44. Check the coolant level and system for leaks. - Decision point: If low, top off and test. If normal, keep diagnosing the ECM.
Common causes
- Faulty coolant temperature sensor
- Damaged wiring or connectors
- Poor connection at the ECM
- Coolant leakage affecting sensor
- Faulty engine control module (rare)
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's moderate severity; you can drive it, but get it fixed soon to prevent overheating issues.
Will this code clear itself?
If the problem is fixed, the code may clear after a few drive cycles.
Why does it pair with SPN 1250?
SPN 1250 is a similar fault for high voltage from the coolant temperature sensor, indicating issues in the same circuit.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
Start guided diagnostic →