GM 34 MAP Sensor Circuit Error Signal Low
How to read it
Code 34 reads as 3 flashes, pause, 4 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 34 mean?
MAP Sensor Circuit Error Signal Low
Common causes of 34
- MAP sensor signal wire shorted to ground
- Failed MAP sensor with low output
- Blocked or kinked vacuum hose on some models
- Faulty ECM reference voltage on rare cases
How to fix 34
- Read MAP voltage through the ALDL port and confirm it stays low
- Inspect the signal wire for chafing to ground
- Apply known vacuum with a hand pump and watch sensor response
- Test reference voltage and ground at the sensor connector
- Replace the sensor only after wiring tests good
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 34. Include your vehicle, the issue and a source if you have one.