What it means
The aftertreatment glow plug heats but exhaust temperature does not rise as expected. Combustion of injected HC may not start.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
On equipped diesels, the aftertreatment glow plug heats the exhaust so fuel from the seventh injector can ignite and support DPF regeneration. P26A0 means the heater is operating but exhaust temperature is not rising as the module expects, suggesting weak heating or insufficient hydrocarbon delivery.
Common causes
Most likely first.
- Aged glow plug heats slowly or unevenly
- HC supply from 7th injector below required
Symptoms
- Glow plug warning light on (often orange coil symbol)
- Hard cold start or no start in cold weather
- White smoke from exhaust during warm-up
How to diagnose it
- Read freeze-frame data and regeneration temperatures to establish whether the temperature rise was low during a commanded aftertreatment heating event.
- Check for related seventh-injector, fuel-delivery, glow plug, and exhaust-temperature sensor codes before isolating this fault.
- Inspect the aftertreatment glow plug, seventh injector connections, and nearby exhaust wiring for damage, leaks, or loose connectors.
- Compare glow plug operation and the temperature sensor readings before and during a commanded test with the manufacturer's specification.
- If the heater response is sound, check seventh-injector delivery using the manufacturer's procedure to determine whether hydrocarbon supply is inadequate.
Common fixes
- Repair loose or damaged connectors at the glow plug, temperature sensor, or seventh injector.
- Replace a glow plug that heats too slowly or unevenly when test results confirm it is faulty.
- Repair the seventh-injector supply or replace the injector if its delivery is below specification.
- Replace a temperature sensor only if its readings fail the specified plausibility checks.
Can I keep driving?
Avoid relying on the vehicle for long trips if the glow plug warning, hard starting, or white smoke persists; cold starts may become unreliable and regeneration may fail. Have it checked promptly if smoke is heavy or the engine will not start.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.