Vauxhall P0402

EGR flow excessive on Vauxhall diesel — Z19DTH and A20DTH stuck-open EGR from carbon build-up.

Vauxhall P0402 — EGR flow excessive on Vauxhall diesel — Z19DTH and A20DTH stuck-open EGR from carbon build-up. Typical UK independent garage cost: £220–£900.

What actually causes P0402 on a Vauxhall

Astra H 1.9 CDTi Z19DTH: EGR valve is a known carbon-trap and sticks open on cars over 80k miles. Insignia 2.0 CDTi A20DTH: EGR cooler cracks internally are more common than valve failure — same symptom, different fix.

Vauxhall engines that log P0402

• 1.9 CDTi Z19DTH (Astra H, Vectra C, Zafira B)
• 2.0 CDTi A20DTH (Insignia, Astra J)
• 1.7 CDTi A17DTS

How we diagnose P0402 on a Vauxhall

1. Tech2/OP-COM live EGR position and MAF flow
2. Remove valve, inspect seat and pintle for carbon
3. Pressure-test EGR cooler on Insignia platform
4. Clean intake, fit OE valve (Pierburg or Delphi)

The common misdiagnosis to avoid

Fitting a new EGR valve on Insignia without pressure-testing the cooler — the cooler crack keeps setting P0402 with a shiny new valve fitted.

Vauxhall P0402 repair cost in the UK

Expect £220–£900 including parts and labour at an independent garage. Main-dealer quotes on Vauxhall are usually higher for the same job, and the spread exists because the cheap cause and the expensive cause throw the same code — pay for the diagnosis before you pay for parts.

Bob's workshop tip

Astra H 1.9 CDTi — Pierburg OE valve. Aftermarket 'improved' valves fail within a year.

Codes usually seen alongside P0402 on Vauxhall

• P0401
• P0403
• P0489

Symptoms drivers report with P0402

• Rough idle, often shaking the gear lever
• Hesitation off the line
• Stalling at junctions
• Possible black smoke at idle
• Engine warning light + power reduction warning

Repairs that clear P0402

• EGR clean or replace
• Sensor inspection

For the generic, all-makes explanation of this code — meaning, every known cause and UK cost bands — see our P0402 guide.

Reading P0402 on a Vauxhall properly

A generic reader will show P0402 and nothing else. What matters is the freeze-frame data stored with it — engine speed, load, coolant temperature and fuel trims at the moment the fault was logged — plus whether any other module on the Vauxhall has logged something at the same time. Codes rarely arrive alone, and the order they were stored in usually points at which one is the cause and which are the consequences.

Clearing P0402 without fixing it

Erasing the code resets the Vauxhall's readiness monitors as well as the light. The fault returns on the next drive cycle if the cause is still there, and in the meantime the incomplete monitors can stop the car passing an emissions check. After a genuine repair, the car is driven until the relevant monitor completes before it is handed back.

Bob's Mechanical Repairs is an independent garage in Birnam, Dunkeld, Perthshire, with 32 years of Bob's experience on the tools. If P0402 is showing on your Vauxhall, bring any scan results with you — we will read the live data ourselves, confirm which cause it actually is, and price the repair before any work starts.