P2CA4: Particulate Filter Pressure Sensor Signals Swapped A/B

What it means

The ECM detects that the particulate filter pressure sensor signals A and B are reversed - low-pressure side reads as high-pressure side and vice versa. Most likely a wiring swap during service.

At a glance

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

How it works

Particulate filter pressure sensors A and B report pressure from opposite sides of the filter so the engine module can judge restriction and manage regeneration. P2CA4 sets when their signals appear reversed, such as the low-pressure side behaving like the high-pressure side, often after their connectors or sensors were swapped during service.

Common causes

Most likely first.

1. Sensor connectors A and B swapped during service
2. Sensors installed in wrong positions

Symptoms

• Check engine light or DPF warning light on
• Power loss / limp mode
• Increased fuel consumption
• Failed forced regeneration attempts

How to diagnose it

1. Record freeze-frame data and compare live readings from pressure sensors A and B at key-on and while the engine is running to see whether the signals are reversed.
2. Inspect both sensor connectors and pressure tubes, tracing each one to its intended high- or low-pressure port.
3. Check whether sensors A and B or their connectors were interchanged during recent filter or sensor service.
4. Verify that each sensor is installed in its intended position and that its wiring reaches the correct circuit.
5. After correcting any swap, confirm that the two readings behave plausibly and check regeneration status with a scan tool.

Common fixes

• Reconnect sensor A and sensor B to their correct connectors.
• Reinstall sensors A and B in their intended positions.
• Correct crossed or misrouted pressure tubes to the proper filter ports.
• Clear the code and verify sensor readings before attempting a regeneration.

Can I keep driving?

Avoid repeated forced regeneration attempts until the sensor connections are corrected; reversed pressure readings can prevent proper filter management. If power is reduced or a DPF warning is on, limit driving and address it soon to avoid worsening filter loading.