Code
P1108
CADILLAC
P — Powertrain
BARO To MAP Sensor Circuit Comparison Too High
Views:
UK: 33
EN: 59
RU: 41
AI status
Completed
Completed
100%
Causes
- Faulty MAP sensor (internal failure or drift)
- Faulty BARO/ambient pressure sensor
- Damaged wiring or poor connector(s) to MAP or BARO (open, short to power, short to ground)
- Corroded or loose sensor pins/terminals
- Intake manifold vacuum leak or leaking vacuum line to MAP
- Blocked MAP sensor port or contamination
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Poor idle quality or rough running
- Reduced engine power or limp mode
- High or low fuel consumption (incorrect fueling)
- Hesitation, stalling or hard starting in some conditions
- Turbo boost control issues on forced-induction engines
What to check
- Read freeze-frame and live data with a scan tool — compare BARO and MAP values at key states (key on/engine off, idle, under load)
- Visual inspection of MAP and BARO connectors, wiring harness, and vacuum lines
- Check for diagnostic trouble codes related to MAP/BARO or intake leaks (e.g., P0106/P0107/P0108)
- Measure sensor supply, reference and signal circuits with a multimeter/scan tool
- Backprobe MAP and BARO sensor terminals to verify voltages and grounds
- Perform a smoke or pressure leak test of intake system and vacuum lines if MAP reads unusually low
Signal parameters
- BARO: steady ambient pressure reading expected; should not vary with engine vacuum. Typical BARO is used as an atmospheric reference.
- MAP: signal varies with intake manifold pressure — lower voltage (or lower pressure reading) at high vacuum (idle/closed throttle), higher voltage (or pressure reading) under load/boost.
- At key-on/engine-off (KOEO) BARO and MAP should be similar (manifold near ambient if throttle open or system allows equalization); large deviation at KOEO may indicate sensor or wiring fault.
- MAP and BARO sensors normally use a 5V reference (or vehicle-specific reference), ground, and a signal circuit; expected signal range commonly spans roughly 0.5–4.5 V depending on pressure and sensor type (verify factory specification).
Diagnostic algorithm
- Retrieve and record freeze-frame data and pending codes. Note engine conditions when code set.
- Clear codes and attempt to reproduce while monitoring live BARO and MAP sensor values with a scan tool (monitor during key-on, idle, and load).
- Visually inspect MAP and BARO connectors and wiring for damage, corrosion, crushed wires, or loose pins. Repair as needed.
- With ignition on, backprobe each sensor: verify presence of correct reference voltage (usually ~5V or vehicle-specific), good ground, and a signal voltage. Compare to factory expected values.
- With engine running, observe MAP signal while applying and releasing vacuum (use hand vacuum pump if available). MAP should respond smoothly; a MAP that does not change likely failed or is blocked.
- Compare BARO reading to known ambient pressure (scan tool or handheld barometer) and to MAP at KOEO/idle. Significant, unexplained differences point to sensor or wiring fault.
- Check for intake and vacuum leaks (smoke test or spray test where safe). Repair any leaks and recheck signals.
- If wiring and vacuum system OK but MAP or BARO readings are out of spec, replace the faulty sensor(s).
- After repair, clear codes and road-test to verify the fault does not return and drivability is restored.
- If problem persists with known-good sensors and good wiring, consider ECM software/operation and consult manufacturer service information.
Likely causes
- Contaminated or clogged MAP sensor port (common)
- Damaged or intermittent wiring between MAP sensor and ECM
- Failed MAP sensor (most likely if wiring checks OK)
- Leaking vacuum hose or intake leak causing MAP to read lower than ambient
- Faulty BARO sensor less likely but possible
Fault status
Status
BARO-to-MAP sensor comparison too high — the ECM detected the BARO (ambient) pressure reading significantly higher than the MAP (manifold) pressure reading beyond allowable threshold. Inspect MAP/BARO sensors, wiring, and intake/vacuum system.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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