Engine Coolant Temperature Sensor 1
Indicates an issue with the engine coolant temperature sensor signal.
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 coolant temperature sensor sends the engine's temperature to the computer. If it sees a value that's too high or low, it triggers a code.
What the computer is actually seeing
The ECM expects a signal between 0.5V (cold conditions) and 4.5V (hot conditions) based on sensor temperatures going from -40°F (-40°C) to 257°F (125°C).
What a healthy reading looks like
0.5V at -40°F, 2.5V at around -32°F, and 4.5V at 257°F.
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 wiring and connectors to the engine coolant temperature sensor for damage or corrosion. Decision: If damaged, repair or replace the wiring/connectors; if not damaged, proceed to step 2.
- 22. Check the coolant level in the reservoir and engine. It should be within the acceptable range. Decision: If low, top it off and monitor for leaks; if adequate, proceed to step 3.
- 33. Using a scan tool, monitor the live data from the coolant temperature sensor. It should reflect current engine temperature accurately. Decision: If readings are erratic or out of expected range, replace the coolant temperature sensor; if readings are normal, check ECM functions.
Common causes
- Failed coolant temperature sensor
- Wiring or connector issues
- Coolant leaks affecting sensor readings
- Faulty engine control module (ECM)
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's moderate severity; you can drive but should fix it soon as it affects engine management.
Will this code come back after clearing?
If the underlying issue isn't resolved, yes.
Why does this code pair with SPN 1243?
SPN 1243 relates to the sensor circuit, both deal with the coolant temperature sensor's performance.
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 →