GM 13 Oxygen Sensor Circuit Open Or No Activity
How to read it
Code 13 reads as 1 flash, pause, 3 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 13 mean?
Oxygen Sensor Circuit Open Or No Activity
Common causes of 13
- Aged or contaminated oxygen sensor with a lazy signal
- Open sensor signal wire or corroded connector
- Exhaust leak near the sensor drawing in air
- Sensor heater fault on heated sensor models
How to fix 13
- Retrieve codes with a paperclip across ALDL pins A and B before starting work
- Watch sensor voltage with a scan tool and confirm it stays fixed near 0.4 volts
- Inspect wiring and ground connections for opens and corrosion
- Repair exhaust leaks ahead of the sensor first
- Replace the sensor only after wiring and leaks test good
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.
Last updated 2026-09-19.
Report a correction for 13. Include your vehicle, the issue and a source if you have one.