Code
P1108
BUICK
P — Powertrain
BARO To MAP Sensor Circuit Comparison Too High
AI status
Completed
Completed
100%
Causes
- Faulty MAP sensor (low signal or intermittent)
- Faulty BARO sensor (high signal or intermittent)
- Open/shorted/damaged wiring or connector for MAP or BARO signal/ground/reference
- Poor sensor ground or 5V reference voltage problem
- Intake vacuum leak or stuck-open component (EGR, PCV) causing low MAP reading
- Blocked MAP port or intake passage
Symptoms
- Check Engine Light (MIL) illuminated
- Poor idle or rough running
- Reduced engine performance or hesitation
- High or erratic fuel trims (observed on scan tool)
- Hard starting or stalling in severe cases
What to check
- Read freeze frame and failure criteria from a scan tool; note whether code set KOEO (key on engine off) or while running
- Compare live BARO and MAP sensor values (pressures and voltages) with a scan tool — note conditions when code sets
- Visually inspect MAP and BARO sensor connectors, wiring harness, and vacuum hoses for damage, disconnection or contamination
- Backprobe sensor signal, ground, and 5V reference with a multimeter/scan tool; check for proper reference and stable ground
- Disconnect MAP vacuum hose to expose sensor to ambient — MAP should track BARO (if it does, suspect vacuum leak or manifold condition)
- Wiggle test wiring while monitoring data for intermittent faults
Signal parameters
- Sensor signal type: 0–5 V analog (verify exact range in factory manual)
- BARO: measures ambient barometric pressure. At key‑on engine‑off BARO and MAP should be essentially equal (difference within manufacturer threshold — typically small, e.g.,
- MAP: at idle will be lower than BARO due to intake vacuum (voltage lower than BARO). If MAP is exposed to ambient (vacuum hose disconnected) it should match BARO.
- Expected 5V reference at sensor pin: stable ~5.0 V (verify spec)
- Sensor ground: near 0 V with good continuity to chassis/PCM ground
Diagnostic algorithm
- Retrieve diagnostic data and freeze frame with a scan tool. Note operating conditions when code set (KOEO or while running).
- With a scan tool monitor BARO and MAP PID values and sensor voltages/pressures. Confirm condition that triggers the comparison failure.
- Perform a simple functional test: with engine off, disconnect the MAP vacuum hose so the MAP sees ambient pressure. BARO and MAP readings should match or be very close. If they match, suspect intake vacuum condition or MAP vacuum source; if they do not match, suspect MAP sensor or wiring.
- Check for proper 5V reference and ground at both MAP and BARO connectors. Repair any missing or unstable reference/ground.
- Backprobe the MAP and BARO signal wires and confirm expected voltages across operating range (apply vacuum to MAP sensor with hand pump to verify response). Use an oscilloscope if available to check noise and transient behavior.
- Inspect and test wiring harness continuity between each sensor and the PCM; repair any opens, shorts to battery or ground, or high resistance joints. Pay attention to connector corrosion and pins.
- Inspect intake system for vacuum leaks (smoke test), blocked MAP port, stuck-open EGR/PCV valves, or other conditions causing excessive manifold vacuum.
- If wiring and intake system check good, swap in a known-good MAP sensor (or BARO if suspicious) if serviceable and repeat tests. Do not swap if sensors are not identical or vehicle-specific.
- If sensors and wiring test good and problem persists, consider PCM input diagnostics — consult factory procedures for PCM testing or replacement.
- After repairs, clear codes and perform a drive cycle to confirm the code does not return.
Likely causes
- MAP sensor signal circuit open, short to ground, or low output
- Vacuum leak or intake restriction causing MAP to read much lower than ambient
- BARO sensor stuck high or shorted to 5V
- Bad sensor ground or 5V reference at sensor connector
Fault status
Status
P1108 — BARO To MAP Sensor Circuit Comparison Too High. The PCM detected that the BARO signal is significantly higher than the MAP signal beyond allowed tolerance.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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