The OBDII codes P0108 and P0101 are common issues in 98 Chevy Blazers, often indicating problems with the Manifold Absolute Pressure (MAP) sensor or its circuit. This article explains these codes, their symptoms, common causes, misdiagnoses, and diagnostic approaches for technicians. While the original text focused on P0108, we’ve expanded to include P0101 for a more comprehensive understanding.
P0108 signifies a high input voltage in the MAP/Barometric Pressure sensor circuit, while P0101 indicates an issue with the MAP sensor range/performance. The MAP sensor measures air pressure in the intake manifold, crucial for the Powertrain Control Module (PCM) to manage fuel-air ratio, ignition timing, and emissions.
Symptoms of P0108 and P0101
Both codes can trigger similar symptoms:
- Illuminated Check Engine Light: The most obvious sign.
- Hard Starting/Poor Fuel Economy: The engine might struggle to start or consume more fuel.
- Reduced Engine Performance: Noticeable power loss or rough idling.
- Hesitation or Stalling: The engine might hesitate during acceleration or stall unexpectedly. (More common with P0101)
Common Causes
Several issues can trigger these codes:
- Faulty MAP Sensor: A defective sensor often requires replacement.
- Vacuum Leaks: Leaks in the intake manifold disrupt pressure readings.
- Wiring/Connection Problems: Damaged or corroded wiring and connections in the MAP sensor circuit.
- Stuck Open EGR Valve: Prevents accurate pressure readings (more relevant to P0108).
- Clogged Air Filter: Restricts airflow and affects pressure readings (more relevant to P0101).
Misdiagnoses to Avoid
- Replacing the MAP sensor without checking for vacuum leaks.
- Overlooking a stuck-open EGR valve as a potential cause for P0108.
- Blaming the MAP sensor when a faulty Idle Air Control Motor is responsible for low idle.
- Assuming P0101 is solely a sensor issue without considering air filter restriction.
Diagnostic Steps for P0108 and P0101
- Retrieve Freeze Frame Data: Capture the conditions when the code was triggered.
- Duplicate Conditions: Recreate the driving scenario to observe live data.
- Monitor MAP Sensor Data: Use a scan tool to observe MAP sensor voltage and compare it to throttle position, RPM, and engine load. Values should fluctuate with engine operation. A consistently high voltage points to P0108. Erratic or out-of-range readings suggest P0101.
- Inspect Vacuum System: Check for leaks using a smoke machine or visual inspection.
- Verify Voltage and Ground: Test the MAP sensor connector for proper 5V reference voltage and ground.
- Test MAP Sensor Output: Use a vacuum pump to test the sensor’s voltage output. The voltage should decrease with increasing vacuum. This helps pinpoint a faulty sensor for both P0108 and P0101.
- Inspect Wiring and Connections: Visually inspect and test the wiring harness for damage or corrosion. Wiggle the connector during testing to identify intermittent issues.
Environmental Impact
Faulty MAP sensors contributing to these codes can lead to increased emissions:
- Hydrocarbons (HCs): Unburnt fuel contributing to smog.
- Carbon Monoxide (CO): A poisonous gas from incomplete combustion.
- Oxides of Nitrogen (NOx): Contribute to smog formation.
Conclusion
Addressing P0108 and P0101 in your 98 Blazer requires a systematic diagnostic approach. By understanding the symptoms, causes, and testing procedures, technicians can accurately pinpoint the problem and restore optimal engine performance and minimize emissions. Remember to consider both mechanical and electrical issues when troubleshooting these codes. A thorough diagnosis is crucial to avoid unnecessary part replacements.
