GM 15 Engine Coolant Temp Sensor Error Low Temp Indicated
How to read it
Code 15 reads as 1 flash, pause, 5 flashes on the check-engine light. Jump terminals A and B on the ALDL connector with the key off, then turn the key on with the engine off and count the check-engine flashes.
New to flash codes? The How to Read GM OBD-I Codes with a Paperclip walks through the test and what the numbers mean. The general OBD-I guide covers the rest.
What does GM code 15 mean?
Engine Coolant Temp Sensor Error Low Temp Indicated
Common causes of 15
- Open coolant temp sensor or unplugged connector
- Broken signal wire or corroded ECM connector pin
- Failed sensor reading far below actual temperature
- Stuck open thermostat keeping the engine cold on some models
How to fix 15
- Inspect the sensor connector and wiring for opens and green corrosion
- Jumper the sensor harness and check whether the scan reading swings hot to prove the circuit
- Measure sensor resistance and compare to the factory temperature chart
- Replace a thermostat stuck open if warm up takes too long
- Clear the code and verify closed loop fuel control returns
Source
Qualified source review
Sources and review
Review: qualified. Read the source limits below.
- GM and Chevrolet OBD1 Trouble Codes (ALDL Fault Code List)
live reference page (troublecodes.net)
Supports: code identity and GM meaning
Fetched directly. Single publisher, so the record is qualified, not verified. Causes and check order are curator-written from the circuit the code names.
https://www.troublecodes.net/gm/
Last updated 2026-09-19.
Report a correction for 15. Include your vehicle, the issue and a source if you have one.