Damaged or chafed wiring in the MAP sensor power supply circuit; Corroded or loose electrical connector at the MAP sensor; Failed manifold absolute pressure sensor with an internal short; Blown fuse or faulty relay supplying the sensor reference voltage; Poor ground connection shared with the MAP sensor circuit; Faulty engine control module driver for the sensor power supply (rare)

DTC codes / Volkswagen codes / P1157

P1157 · VolkswagenManifold Absolute Pressure Sensor Circuit Power Supply Malfunction

P1157 on Volkswagen vehicles indicates that the engine control module has detected a malfunction in the power supply circuit feeding the manifold absolute pressure sensor, which measures intake manifold vacuum and boost pressure. The computer monitors the sensor's reference voltage and flags this code when the supply is out of range, shorted, or intermittent.

SystemPowertrain

Code typeVolkswagen specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illuminated check engine light, often with no other noticeable symptoms
Rough idle or unstable engine speed, especially when cold
Hesitation or stumble during acceleration
Poor fuel economy or rich-running exhaust smell
Reduced engine power or limp mode in some models
Intermittent stalling when coming to a stop

Common causes, most likely first

Damaged or chafed wiring in the MAP sensor power supply circuit
Corroded or loose electrical connector at the MAP sensor
Failed manifold absolute pressure sensor with an internal short
Blown fuse or faulty relay supplying the sensor reference voltage
Poor ground connection shared with the MAP sensor circuit
Faulty engine control module driver for the sensor power supply (rare)

How to diagnose and fix it

Scan all modules and record freeze-frame data to confirm P1157 is the primary fault
Inspect the MAP sensor connector and wiring for corrosion, chafing, or loose pins
Check the fuse and relay that supply power to the MAP sensor circuit
Measure reference voltage at the MAP sensor connector with the key on and compare to specification
Perform a voltage drop test on the power and ground circuits to rule out resistance
Substitute a known-good MAP sensor only after circuit tests pass
Repair or replace damaged wiring, then clear codes and verify the repair with a road test

What most technicians overlook on P1157

A chafed wire harness near the intake manifold or timing cover often causes an intermittent power supply fault that never appears during a static voltage check.
The MAP sensor shares its reference voltage with other sensors on many Volkswagen engines, so a short in a neighbouring sensor can set P1157 without the MAP sensor itself being faulty.
Aftermarket air intake or boost gauge installations frequently disturb the MAP sensor wiring, creating a power supply malfunction that looks like a failed sensor.
A weak battery or failing voltage regulator can cause the reference voltage to drop below threshold intermittently, setting P1157 along with other unrelated codes.
Clearing the code without repairing the circuit often leads to a repeat failure because the ECM re-learns the fault only after a complete drive cycle.

Can I keep driving with P1157?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration or towing because a faulty MAP sensor signal can cause poor fuel mixture and reduced power. If the engine runs rough or stalls, stop driving and arrange a tow.

Tools that help

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Guidance is general and written for Volkswagen vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.