Chafed or shorted signal wire between the MAP sensor and ECU contacting a battery-positive wire; Failed manifold absolute pressure sensor with an internal short to its reference voltage; Corroded or water-contaminated connector pins at the MAP sensor or ECU; Damaged wire harness near the intake manifold or firewall where vibration causes insulation wear; Faulty engine control module driver circuit, though rare; Aftermarket wiring repairs or accessories incorrectly tapped into the sensor circuit

DTC codes / Volkswagen codes / P1155

P1155 · VolkswagenManifold Absolute Pressure Sensor Circuit Short To B+

Q: What does code P1155 mean?

Manifold Absolute Pressure Sensor Circuit Short To B+. P1155 on Volkswagen vehicles means the engine control module has detected a short to battery voltage on the signal circuit of the manifold absolute pressure sensor, which measures intake manifold pressure for load calculation. The computer expects a voltage within a calibrated range but sees a constant high voltage near B+ instead, so it flags the circuit as faulty.

P1155 on Volkswagen vehicles means the engine control module has detected a short to battery voltage on the signal circuit of the manifold absolute pressure sensor, which measures intake manifold pressure for load calculation. The computer expects a voltage within a calibrated range but sees a constant high voltage near B+ instead, so it flags the circuit as faulty.

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 as the ECU substitutes a default pressure value
Poor throttle response or hesitation during acceleration
Increased fuel consumption from incorrect load calculation
Intermittent stalling or hard starting in severe cases
Possible reduced power or limp mode on some models

Common causes, most likely first

Chafed or shorted signal wire between the MAP sensor and ECU contacting a battery-positive wire
Failed manifold absolute pressure sensor with an internal short to its reference voltage
Corroded or water-contaminated connector pins at the MAP sensor or ECU
Damaged wire harness near the intake manifold or firewall where vibration causes insulation wear
Faulty engine control module driver circuit, though rare
Aftermarket wiring repairs or accessories incorrectly tapped into the sensor circuit

How to diagnose and fix it

Scan all modules and record freeze-frame data to confirm P1155 is active and not a ghost code
Visually inspect the MAP sensor connector and harness for chafing, corrosion, or moisture intrusion
Disconnect the MAP sensor and measure voltage on the signal wire with the key on; a constant B+ reading confirms a short
Isolate the circuit by wiggling the harness and checking for voltage changes while monitoring the signal wire
Repair any damaged wire section with proper solder and heat-shrink, then clear codes and verify the signal voltage returns to normal
If the circuit is intact, substitute a known-good MAP sensor and recheck live data
Perform a final road test with live data to confirm the code does not return and pressure readings track engine load

Why a MAP short mimics other faults

A short to B+ on the MAP signal wire often causes the ECU to default to a calculated pressure value, so the engine may run almost normally and hide the fault from the driver.
Technicians sometimes replace the MAP sensor first, but a chafed signal wire near the intake manifold is the more common root cause on high-mileage Volkswagen engines.
Water ingress into the sensor connector after engine washing or heavy rain can create a temporary short that sets P1155 only under wet conditions.
The same short can trigger companion codes for mixture adaptation or turbocharger control because the ECU misjudges engine load, so always diagnose P1155 before chasing those codes.
A faulty ECU is rarely the cause, but a shorted sensor circuit can damage the ECU driver if left unrepaired, so do not ignore the code indefinitely.

Can I keep driving with P1155?

You can usually drive the vehicle to a workshop, but avoid aggressive acceleration and long trips because the ECU is running on default pressure values that can affect fuel mixture and emissions. If the engine runs rough or stalls, stop driving and arrange a tow to prevent further damage.

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.