OBD-II reference

All 9.533 generic OBD-II codes, explained in detail.

Causes, inspection steps and sources — a comprehensive DIY archive. Created and maintained with love for the detail. Good luck and have fun!

Powertrain generic / SAE

P026F

Coolant Thermostat Performance

Thermostat does not regulate coolant temperature in the expected range. Often stuck open (slow warmup) or stuck closed (overheat).

SystemPowertrain
Typegeneric / SAE
GroupP0
Range / number2 / 6F

Possible causes

  • Thermostat stuck high

Inspection / repair

  • Difficulty: medium
  • DIY: possible
  • Estimated cost: 60–400 €
  • Estimated time: 0.5–3 h
  • Component: thermostat
  • MIL / check engine light
  • emissions-relevant
  • drive cycle required

Sources

References

sae:J2012

How to read OBD-II codes

The first letter names the vehicle system, the second digit distinguishes generic from manufacturer-specific, the remaining digits group fault area and number.

PPowertrain: engine, transmission, emissions
BBody: chassis trim, comfort, interior
CChassis: suspension, brakes, steering
UNetwork: CAN, control modules, communication