GM 33 MAP Sensor Circuit Error Signal High
How to read it
Code 33 reads as 3 flashes, 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 33 mean?
MAP Sensor Circuit Error Signal High
Common causes of 33
- MAP sensor vacuum hose cracked or disconnected
- Failed MAP sensor reading high voltage
- Open sensor ground circuit
- Intake vacuum leak lowering manifold vacuum
How to fix 33
- Inspect the MAP vacuum hose for cracks and secure connections
- Read MAP voltage through the ALDL port at idle and with the engine off
- Test sensor voltage against known vacuum readings
- Repair vacuum leaks before replacing the sensor
- Replace the sensor only if voltage stays high with good vacuum applied
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 33. Include your vehicle, the issue and a source if you have one.