Diesel Particulate Filter Efficiency Below Threshold (Bank 1)

What it means

The diesel particulate filter (DPF), which traps soot from the exhaust, is not filtering properly. The ECU sees too little pressure difference across it, which can mean a cracked or removed filter, or a sensor problem.

Symptoms

• Check engine or DPF light on
• Black soot at the tailpipe
• Possible reduced power

Probable causes

Most likely first

1. 1Cracked or damaged DPF
2. 2Faulty DPF pressure sensor or its hoses
3. 3Exhaust leak before the DPF

How to diagnose it

Work through these in order before buying parts

1. 1Record the code and its freeze frame data (speed, load, temperature when it set), then clear it and see if it comes back.
2. 2Check the DPF pressure sensor hoses for cracks or swapped connections.
3. 3Check DPF differential pressure on live data at idle and higher RPM.
4. 4Look for soot at the tailpipe (a working DPF leaves it clean).
5. 5Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.

Common fixes

• Replace the DPF pressure sensor or hoses
• Replace the DPF