P1156

Code

VOLKSWAGEN P — Powertrain

Manifold Absolute Pressure Sensor Circuit Open/Short To Ground

Brand: VOLKSWAGEN

Type: P — Powertrain

Views: UK: 31 EN: 174 RU: 73

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Page language: EN

Causes

Broken or chafed wiring in MAP sensor harness
Disconnected, corroded, or damaged MAP sensor connector
MAP sensor internal failure (open or shorted output)
Short to ground caused by aftermarket wiring or repairs
Poor or missing power/ground to sensor (blown fuse, bad ECU ground)
ECU input fault (rare)

Symptoms

Check Engine Light (MIL) illuminated
Rough idle, hesitation, or stalling
Poor drivability and reduced engine power
Hard starting or increased cranking time
High or erratic fuel consumption
Turbo boost control issues (on forced-induction engines)

What to check

Read fault code(s) and freeze-frame data with a factory scan tool or OBD-II reader
Check live MAP sensor PID/signal while key on and while engine running
Visually inspect MAP sensor, connector, and wiring for damage, corrosion, or oil contamination
Back-probe and measure reference voltage, signal voltage, and ground at the sensor connector
Perform continuity and resistance checks from sensor pins to ECU connector with wiring disconnected
Wiggle test harness while monitoring MAP signal for intermittent faults

Signal parameters

Reference supply: approx. 5 V (vehicle-specific — verify with factory data)
Sensor signal: typically ~0.5–4.5 V (proportional to absolute intake pressure) — approximate values:
- High vacuum / idle (~20–40 kPa): ~1.0–2.0 V
- Atmospheric (~95–105 kPa): ~4.0–4.5 V
- Boost (>100 kPa absolute): signal may approach upper range (vehicle dependent)
Sensor ground: near 0 V; good chassis/ECU ground continuity usually < 1 ohm

Diagnostic algorithm

Verify the code and note freeze-frame/live MAP PID with scan tool. Confirm symptom reproducibility.
Visually inspect sensor and harness for obvious damage, oil intrusion, or disconnected connector.
With ignition ON (engine OFF), back-probe connector: verify reference voltage (≈5 V) and ground presence.
Measure MAP signal voltage with ignition ON and engine running. Compare to expected ranges; note if signal is ~0 V (short to ground) or absent.
If signal is ~0 V, isolate the wiring: disconnect sensor and check signal wire continuity to ECU pin. If continuity to ECU ground exists, inspect for short to chassis ground along harness.
Check continuity from sensor ground pin to chassis/ECU ground; repair any high-resistance or open ground.
Wiggle harness while monitoring for intermittent changes. Repair chafing, replace damaged sections, or re-pin connectors as required.
If wiring and connector check good, bench-test or replace MAP sensor with a known-good unit and re-scan.
If replacement sensor does not clear fault and wiring is confirmed good, suspect ECU input fault — verify with manufacturer procedures before replacing ECU.
After repairs, clear codes and perform a road test and re-check for reappearance of the code and proper MAP PID behavior.

Likely causes

Corroded/loose connector pins at MAP sensor
Open signal wire between MAP and ECU (broken at harness rub-through or connector)
Signal wire shorted to chassis ground (pinched or contact with metal)
Failed MAP sensor electronics
Faulty ground at sensor or ECU

Fault status

⚠️ Status

Manifold Absolute Pressure (MAP) Sensor Circuit Open/Short to Ground detected. ECU flagged an invalid or missing MAP signal; stored as P1156.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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P1156 — Manifold Absolute Pressure Sensor Circuit Open/Short To Ground