EVAP charcoal canister codes

How its codes differ

• Leak codes (P0455, P0442, P0456) can come from the canister itself, for example a cracked housing or a leaking weld; GM has a bulletin for P0442 from a canister weld leak.
• Vent and purge codes (P0446, P0449, P0441, P0496) concern the valves attached to the canister rather than the canister itself, although dust or liquid fuel in the canister can affect them.
• Liquid fuel reaching the canister, for example from repeatedly topping off the tank, can saturate it; Mazda recalled some Mazda3 models because liquid fuel could enter the canister, causing a check engine light, rough idle or stalling and a fuel leak risk.
• P0497 (low purge flow) can follow a canister soaked with liquid fuel; this is a lead to test rather than a common cause.

Codes

• P0455

  EVAP system large leak detected

  Severity: Monitor

• P0442

  EVAP system small leak detected

  Severity: Monitor

• P0456

  EVAP system very small leak detected

  Severity: Monitor

• P0440

  EVAP system fault (general)

  Severity: Monitor

• P0441

  EVAP purge flow incorrect

  Severity: Monitor

• P0446

  EVAP vent control performance problem

  Severity: Monitor

• P0449

  EVAP vent valve circuit fault

  Severity: Monitor

• P0496

  EVAP purge flow when purge should be off

  Severity: Monitor

• P0443

  EVAP purge valve circuit fault

  Severity: Monitor

• P0497

  EVAP system low purge flow

  Severity: Monitor

Signs it's failing

• Check engine light with EVAP leak or flow codes
• Fuel smell
• Hard filling or the pump nozzle clicking off early
• Rough idle or stalling if liquid fuel has reached the canister

How to test it

1. Stop filling the tank at the first click of the pump nozzle; topping off can push liquid fuel into the canister. (Low risk)

2. Check for open recalls on your vehicle using its VIN. (Low risk)

3. Smoke testing and canister inspection are shop jobs. (Best left to a shop)

   Warning: Fuel and fuel vapour are flammable. Work with the engine off and cool, in a ventilated area, with no smoking, sparks or flames nearby.

After the repair

• Allow several days of normal driving for the EVAP monitor to run again; it needs particular fuel level and temperature conditions, so it is often the last monitor to complete.
• Clear codes only after the repair, then drive normally over several days with both city and highway driving so the readiness monitors can complete; clearing codes or disconnecting the battery resets them to not ready, which fails an emissions test.