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P2403 – Evaporative Emission System Leak Detection Pump Sense Circuit/Open (OBD2)

P2403 means "Evaporative Emission System Leak Detection Pump Sense Circuit/Open". The control unit sees an open circuit: the electrical connection to the evaporative emission (EVAP) system is interrupted, so no current can flow when the component is commanded or read.

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P2403 quick summary

Fault codeP2403
MeaningEvaporative Emission System Leak Detection Pump Sense Circuit/Open
SystemPowertrain (Engine & Transmission)
VehiclesGeneric OBD2
SeverityLow
Can I drive?Yes. EVAP faults rarely affect driving, but fuel vapour escapes and the car may fail an emissions test. A strong fuel smell should be checked promptly.
Repair cost€0 – €400

How the EVAP system works

The evaporative emission system stores fuel vapour from the tank in a charcoal canister and burns it in the engine, so it does not escape into the air; these codes cover leaks, purge flow and the EVAP valves.

Fuel vapour from the tank is collected in an activated charcoal canister. When the engine is warm, the purge valve opens and the engine draws the vapour in and burns it. A vent valve lets fresh air into the canister; on many cars it can close so the system can be leak-tested.

The control unit regularly tests the system: it seals it, applies vacuum (or pressure with a leak detection pump) and watches whether it holds. Small and large leak codes (P0442, P0455, P0456) mean the system did not hold. Other codes cover the purge valve, vent valve, pressure sensor and purge flow.

By far the most common cause of a leak code is a fuel cap that is loose, missing or has a damaged seal. Other causes are cracked hoses, a leaking canister or valves that stick. Most EVAP faults do not affect how the car drives, but a purge valve stuck open can cause rough idle and hard starting after refuelling.

Symptoms of P2403

  • Check Engine light on
  • Fuel smell around the car
  • Rough idle or hard starting after refuelling (purge valve stuck open)
  • Fuel pump nozzle clicks off repeatedly when refuelling (vent problem)
  • Usually no driving symptoms

Most common causes of P2403 (most likely first)

Mechanic's Pro Tip

Fix the cheap things first: a new fuel cap seal costs very little and solves a large share of small-leak codes. And do not keep filling after the nozzle clicks off – overfilling pushes liquid fuel into the charcoal canister and ruins it.

  1. 1.Unplugged, loose or corroded connector

    Most likely

    Often after previous repair work in the area.

  2. 2.Broken wire in the harness

    Typical at bends, near the engine mounts and where the harness rubs on brackets.

  3. 3.Burnt-out winding or internal break in the evaporative emission (EVAP) system

  4. 4.Loose, missing or damaged fuel cap

    The most common cause of leak codes.

  5. 5.Cracked EVAP hoses or connections

    Plastic lines become brittle with age.

  6. 6.Faulty purge valve (canister purge solenoid)

    Sticks open or closed, or has an electrical fault.

  7. 7.Faulty vent valve or leak detection pump

Step-by-step diagnostic guide

  1. 1

    Check the fuel cap

    Check that the fuel cap is present, tight and the seal is not cracked. Clear the codes and see if they return.

  2. 2

    Measure resistance and continuity

    Unplug the evaporative emission (EVAP) system and measure its resistance across the terminals. An infinite (OL) reading confirms an internal break. If the component is fine, check each wire back to the control unit for continuity.

    Multimeter: Solenoids and heaters typically read a few ohms to a few dozen ohms; "OL" means open. Wire continuity: below about 1 Ω.

  3. 3

    Read codes and run the EVAP test

    Read all codes and, where the scan tool supports it, run the EVAP system test.

  4. 4

    Smoke-test the system

    A smoke test through the service port or vent side finds small leaks in hoses, the canister and the filler neck.

  5. 5

    Test the purge and vent valves

    Command the valves with the scan tool and check that they open and close. Check their resistance and wiring.

    Multimeter: Typical purge valve resistance: about 20–35 Ω. With the engine idling and the purge valve not commanded, there should be no vacuum at the canister side.

  6. 6

    Repair and verify

    Replace the faulty part and drive the car through a full EVAP test cycle (often requires a cold start and a certain fuel level) to confirm the repair.

Frequently asked questions

Can I keep driving with P2403?

Yes. EVAP faults rarely affect driving, but fuel vapour escapes and the car may fail an emissions test. A strong fuel smell should be checked promptly.

How much does it cost to fix P2403?

Typical repair costs are 0 € – 400 €, depending on the cause and the vehicle. The most common fixes are: unplugged, loose or corroded connector; broken wire in the harness; burnt-out winding or internal break in the evaporative emission (EVAP) system. Always confirm the cause with the tests above before buying parts.

Can a loose fuel cap really turn on the Check Engine light?

Yes. The control unit tests the EVAP system for leaks, and an unsealed fuel cap is the most common reason for a leak code.

Why does the code take days to clear after the repair?

The EVAP test only runs under specific conditions (for example a cold start and a certain fuel level). The code clears after the test passes, which may take several drive cycles.

What is the difference between P2403 and similar codes?

P2403 belongs to a group of codes for the same component that differ in the type or location of the fault: P2400 – Evaporative Emission System Leak Detection Pump Control Circuit/Open; P2401 – Evaporative Emission System Leak Detection Pump Control Circuit Low; P2402 – Evaporative Emission System Leak Detection Pump Control Circuit High; P2404 – Evaporative Emission System Leak Detection Pump Sense Range/Performance; P2405 – Evaporative Emission System Leak Detection Pump Sense Circuit Low; P2406 – Evaporative Emission System Leak Detection Pump Sense Circuit High. The tests on this page apply to the whole group; the type of fault tells you where to start.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.