What Does P1156 Mean?
This code indicates the Manifold Absolute Pressure (MAP) sensor circuit has an open circuit or a short to ground. The MAP sensor provides critical engine load data to the PCM by measuring intake manifold vacuum/pressure. When the signal wire is open or shorted to ground, the PCM receives a fixed low voltage reading that does not correspond to actual manifold pressure, causing incorrect fuel delivery and ignition timing calculations.
Safety Warning
Incorrect MAP readings can cause severe driveability issues including stalling, rough idle, and loss of power. The vehicle may enter limp mode, which could be hazardous in traffic situations requiring normal acceleration.
Common Causes
30%
Damaged or broken signal wire between the MAP sensor and PCM (open circuit)
25%
MAP sensor signal wire chafed and shorted to chassis ground
20%
Failed MAP sensor with internal short or open
15%
Corroded or loose MAP sensor connector pins
10%
Cracked or disconnected vacuum hose to the MAP sensor
Diagnostic Steps
1
With the key on and engine off, check MAP sensor voltage at the PCM connector; it should read approximately 4.5-4.8V (atmospheric pressure). A reading near 0V confirms a short to ground or open signal.
2
Inspect the MAP sensor connector for bent pins, corrosion, or moisture; ensure the 5V reference, signal, and ground wires are all connected.
3
Use an ohmmeter to check for continuity of the signal wire from the MAP sensor connector to the PCM, and check for shorts to ground.
4
If the sensor has a vacuum hose, verify the hose is connected and not cracked, collapsed, or plugged with carbon.
5
Substitute a known-good MAP sensor and check if the voltage reading returns to normal; replace if confirmed faulty.
Estimated Repair Cost
$80 - $300
Parts + labor, varies by vehicle and location
This code indicates the Manifold Absolute Pressure (MAP) sensor circuit has an open circuit or a short to ground. The MAP sensor provides critical engine load data to the PCM by measuring intake manifold vacuum/pressure. When the signal wire is open or shorted to ground, the PCM receives a fixed low...
The most common cause of P1156 (Manifold Abs.Pressure Sensor Circ. Open/Short to Ground) is: Damaged or broken signal wire between the MAP sensor and PCM (open circuit)
Typical repair costs for P1156 range from $80 to $300, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Incorrect MAP readings can cause severe driveability issues including stalling, rough idle, and loss of power. The vehicle may enter limp mode, which could be hazardous in traffic situations requiring normal acceleration.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1156 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel / Air Metering
Difficulty
Type
Manufacturer
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