Code 3: Map Sensor
NOTE:
For wiring diagrams, see WIRING DIAGRAMS
article. For vacuum diagrams, see VACUUM DIAGRAMS
article.
- Turn ignition off. Disconnect alternator sense fuse in under-hood relay box for 10 seconds to reset ECU. Start engine and observe CHECK ENGINE light and ECU LED for code indication. If light is off and LED does not indicate any codes, problem is intermittent. Check for poor or loose connection at MAP sensor connector. Test drive and check again.
- If light is on and LED indicates Code 3, turn ignition off. Connect 3-Pin Test Harness (07GMJ-ML80100 ) between MAP sensor and sensor harness. Turn ignition on. Measure voltage between Red (positive) and Green (negative) wires. If reading is not about 5 volts, measure between Red wire and ground.
- If this reading is about 5 volts, repair open in Green/White wire between ECU terminal C16 and MAP sensor. If reading is not about 5, turn ignition off. Connect ECU test harness. Refer to Figure . Turn ignition on. Measure voltage between terminals C15 and C16.
- If voltage is about 5 volts, repair open in Yellow/White wire between C15 and MAP sensor. If voltage is not about 5 volts, substitute a known good ECU and recheck. If voltage is now correct, replace original ECU. After measuring between Red (positive) and Green (negative) wires in step 2), if voltage is about 5 volts, measure between White (positive) and Green (negative) wires.
- If reading is not about 3 volts, replace MAP sensor or repair short in White wire between ECU terminal C11 and MAP sensor. If measured voltage is about 3 volts, turn ignition off. Connect ECU test harness between ECU and ECU connectors.
- Turn ignition on. Measure voltage between terminal C11 (positive) and C16 (negative). If voltage is not about 3 volts, repair open White wire between ECU terminal C11 and MAP sensor. If there is about 3 volts present, substitute a known good ECU. If condition goes away, replace original ECU.