P2A0C: Manifold Absolute Pressure Sensor B Circuit Low

What it means

Voltage on the MAP B signal line is below the expected window. Wire shorted to ground or sensor short.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

MAP B converts intake manifold pressure into an electrical signal for the ECM. This code sets when the signal voltage falls below the expected range, pointing to a signal short to ground, an internally shorted sensor, or a poor connection that pulls the signal down.

Common causes

Most likely first.

1. Signal wire shorted to ground
2. Internal sensor short
3. Connector pins corroded - high contact resistance

Symptoms

• Check-engine light
• Rough idle
• Poor acceleration

How to diagnose it

1. Record freeze-frame data and compare MAP B with the primary MAP reading and throttle position to confirm the low signal occurs on the secondary channel.
2. Inspect the MAP B connector for corrosion, pushed-back pins, moisture, and loose fit, then check the harness for chafing against ground.
3. Using the wiring diagram, check the signal wire for a short to ground and verify sensor power and ground connections.
4. Measure MAP B signal behavior with the sensor connected and disconnected as appropriate for the vehicle procedure to distinguish a harness short from a sensor fault.
5. Compare circuit and sensor readings with the manufacturer's specification before replacing parts.

Common fixes

• Repair a signal wire shorted to ground.
• Clean or repair corroded or loose MAP B connector terminals.
• Restore a faulty sensor ground or power connection.
• Replace MAP B if the signal remains low with a sound harness and connections.

Can I keep driving?

Avoid long trips or demanding acceleration because the ECM may misjudge engine load, causing rough running or weak response. If the engine stalls or becomes difficult to control in traffic, stop driving.