Code
P1240
MINI
P — Powertrain
Manifold absolute pressure (MAP) sensor 2 - signal too low at idle
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EN: 11
RU: 7
AI status
Completed
Completed
100%
Causes
- Faulty MAP sensor #2 (internal failure or contamination)
- Open/short in sensor signal wire (short to ground or low resistance path)
- Poor connector connection or corroded pins at sensor or ECU
- Loss of sensor reference voltage (5 V) or bad ground at sensor
- Blocked/plugged sensor port or tubing (if remotely mounted)
- Intake or vacuum leak affecting expected manifold pressure readings
Symptoms
- MIL/Check Engine Light on
- Rough or unstable idle
- Reduced drivability (hesitation, poor throttle response)
- Poor fuel economy or incorrect fueling at idle
- Possible turbo/boost control issues on forced-induction engines
What to check
- Read freeze frame and live data for MAP2 and compare to MAP1 (look for discrepancy)
- Visually inspect MAP sensor, connector, and wiring for damage, corrosion, or looseness
- Inspect sensor mounting port and tubing for blockage or contamination
- Verify reference voltage (typically ~5 V) and good ground at MAP2 connector
- Backprobe sensor output with engine at idle and note voltage/pressure
- Perform a wiggle test on wiring while watching live data for intermittent changes
Signal parameters
- Key ON, engine OFF (manifold = atmospheric): MAP2 output ≈ 4.4–5.0 V (varies by sensor)
- At idle (engine vacuum ~20–40 kPa depending on engine): MAP2 output typically ≈ 0.5–1.5 V (manufacturer-specific)
- MAP2 should change smoothly with throttle — voltage falls with increasing vacuum and rises toward atmospheric pressure
- Difference between MAP1 and MAP2 should be within manufacturer tolerance (typically
Diagnostic algorithm
- Retrieve DTC data and freeze frame. Note engine rpm, load, temp and MAP1 vs MAP2 readings when code set.
- Inspect sensor and harness visually. Repair any obvious damage or corrosion to connector/pins.
- With ignition ON, measure reference voltage at MAP2 connector (expect ~5 V). If missing, trace power feed to ECU/fuse.
- With engine running at idle, backprobe MAP2 signal wire and measure voltage. Compare to expected idle voltage and to MAP1.
- If signal is low, check continuity and resistance of signal wire to ECU; check for short to ground.
- Inspect/clean sensor inlet/port and any vacuum hose to sensor. Clear any blockage and retest.
- Swap MAP2 with a known good identical sensor (or substitute MAP1 if identical and allowed) to see if fault follows the sensor.
- If wiring and sensor test good but code persists, test ECM input circuit or consult manufacturer data for ECU diagnostics before replacing ECU.
- After repairs, clear codes and perform a test drive to verify code does not return and MAP2 behaves correctly in live data.
Likely causes
- Damaged or chafed signal wire shorted to ground
- Corroded or loose connector at MAP sensor
- MAP sensor failed internally (stuck low output)
- Blocked vacuum/pressure port or foreign debris inside sensor inlet
- Low or missing 5 V reference due to power/ECU connector issue
Fault status
Status
P1240 — Manifold Absolute Pressure (MAP) Sensor 2: signal too low at idle. The ECM detected MAP2 voltage below the expected threshold during idle monitoring. Check sensor, wiring, reference voltage and vacuum/port integrity.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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