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
- Tech2/OP-COM live EGR position and MAF flow
- Remove valve, inspect seat and pintle for carbon
- Pressure-test EGR cooler on Insignia platform
- 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.