Code
P1237
MINI
P — Powertrain
Manifold absolute pressure (MAP) sensor 2 - low input
Views:
UK: 4
EN: 4
RU: 3
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring between MAP sensor 2 and the ECM (short to ground)
- Corroded, loose or damaged connector at the MAP sensor
- Failed MAP sensor (internal fault)
- Incorrect or missing 5V reference or ground at the sensor
- Intake vacuum leak or damaged vacuum port tubing (causes unexpected readings)
- ECM input circuit fault (less common)
Symptoms
- Check Engine Light (MIL) illuminated
- Poor idle, stalling or rough running
- Reduced engine power or limp mode under boost conditions
- Poor fuel economy, hesitation on acceleration
- Possible hard start or no start if signal is invalid
What to check
- Retrieve freeze frame and live data with a scan tool. Observe MAP sensor 2 voltage/pressure vs MAP sensor 1 (if present) and BARO.
- Key ON Engine OFF (KOEO) check: MAP2 voltage should approximate barometric pressure reading and be similar to MAP1.
- Backprobe the sensor connector: verify 5V reference, ground, and signal voltage.
- Wiggle test the wiring harness and observe live data for intermittent changes.
- Inspect connector for corrosion, bent pins, or water ingress.
- Perform continuity and short-to-ground tests on the signal and reference wires between sensor and ECM.
Signal parameters
- Typical MAP sensor analog signal: approximately 0.5–4.5 V across operating range (manufacturer-specific values may vary).
- Low input is generally considered when the signal is below ~0.2–0.3 V or is significantly lower than MAP1/BARO readings for KOEO.
- At KOEO the MAP signal should read near barometric pressure (sensor-dependent).
- During idle and load the signal changes proportionally with manifold pressure; compare MAP2 to MAP1 for consistency.
Diagnostic algorithm
- Verify the DTC and any related codes. Capture freeze frame and live MAP1, MAP2, and BARO data.
- KOEO: Confirm MAP2 voltage ~BARO and similar to MAP1. If MAP2 is low while MAP1 and BARO are normal, suspect sensor2/harness.
- Backprobe sensor connector: verify 5V reference present and stable, good ground, and measure signal voltage.
- If 5V or ground missing or unstable, trace and repair wiring to ECM. Confirm continuity and check for short to ground on the signal wire.
- If reference and ground are good but signal is low, disconnect the sensor and measure output at the sensor connector with connector disconnected (to rule out sensor loading).
- Swap MAP sensors (if identical and applicable) or install a known-good sensor and re-check the signal and codes.
- Inspect intake tubing and vacuum lines serving the sensor for leaks or crushes that could cause abnormal readings.
- If wiring and sensor check good but the fault persists, check ECM input circuit and perform harness-to-ECM continuity and resistance checks; consider ECM replacement only after confirming other causes.
- Clear codes and perform road test to verify repair.
Likely causes
- Damaged/shorted harness or connector to MAP sensor 2
- Failed MAP sensor 2
- Loss of sensor reference (5V) or ground
- Intake leak or plumbing disconnected to the sensor
Fault status
Status
ECM detected MAP sensor 2 signal voltage below expected range. Code stored (may be pending or confirmed). Possible drivability impact; further inspection required.
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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