P0402

What P0402 means

This is a generic OBD-II powertrain code. The definition is standardised, but the diagnostic path and the parts involved differ by engine — the detail below is specific to 6.7L Power Stroke, 6.6L L5P Duramax, 6.7L Cummins.

How a technician diagnoses it

1. 1

   Read freeze frame and note whether the fault set at idle, at cruise, or under load. That single data point narrows the list considerably.

   Tool: Scan tool

2. 2

   Command the EGR valve closed and open with a bidirectional tool and compare commanded to actual position through the full sweep.

   Tool: Bidirectional scan tool

3. 3

   Remove and physically inspect the EGR valve. On these engines carbon is visible and conclusive — a valve that will not seat by hand will not seat in service.

4. 4

   Clean the MAF sensor and inspect the intake air temperature and manifold pressure sensors for soot fouling before replacing anything.

   Tool: MAF-safe cleaner

5. 5

   Pressure test the EGR cooler for internal leaks if coolant loss, white smoke, or a sweet exhaust smell is present.

   Spec: TODO(verify): cooler pressure test procedure and hold spec per manufacturer

6. 6

   Inspect the intake manifold and charge air path for carbon restriction. Cleaning a valve into a plugged intake is temporary.

7. 7

   After repair, clear codes and complete a full drive cycle to confirm the monitor runs and passes rather than assuming it is fixed because the light is off.

Parts and labour

Labour priced at provisional national placeholder — TODO(verify), not yet from our collected dataset. How we build these numbers.

Can I keep driving?

Yes, in most cases — but not comfortably and not efficiently. Excessive EGR raises soot production, which loads the particulate filter faster and can chain into DPF and regeneration faults. If the engine is stumbling badly at idle or smoking heavily, get it in before it turns into a filter bill on top of a valve bill.