P2402 – EVAP Leak Detection Pump Control Circuit High: Complete Technical Guide
System Overview and Technical Specifications
The Evaporative Emission Control (EVAP) system is designed to prevent gasoline vapors from escaping into the atmosphere. The Leak Detection Pump (LDP) is a critical component that pressurizes the fuel system to check for leaks. The P2402 code specifically relates to the electrical control circuit between the PCM and the LDP.
EVAP System Voltage Specifications
| Circuit State | Expected Voltage | Tolerance | Measured At |
|---|---|---|---|
| Control Circuit – Normal (Key ON, Engine OFF) | 0.5V – 1.5V | ±0.2V | LDP Connector |
| Control Circuit – Active (Pump Running) | 2.5V – 4.5V | ±0.5V | LDP Connector |
| Control Circuit – Fault (P2402) | > 4.8V | N/A | PCM Pin |
| Power Supply Circuit | 12.0V – 14.5V | ±0.5V | LDP Power Pin |
| Ground Circuit Resistance | < 0.5Ω | Maximum | LDP Ground to Battery |
Detailed Diagnostic Trouble Code Information
P2402 Code Parameters and Triggers
The PCM monitors the LDP control circuit voltage through an internal voltage divider network. When the PCM commands the LDP ON (by grounding the control circuit through a low-side driver), it expects to see a specific voltage drop. P2402 is set when:
- The PCM detects voltage > 4.8V on the control circuit for more than 5 seconds
- The condition occurs during two consecutive drive cycles
- The EVAP monitor runs and fails the circuit check
- The vehicle speed is typically > 15 mph for the test to initiate
Complete Related Error Code Matrix
| DTC Code | Description | Relationship to P2402 | Diagnostic Priority |
|---|---|---|---|
| P2401 | EVAP Leak Detection Pump Control Circuit Low | Opposite circuit condition – indicates short to ground | High – Often diagnosed together |
| P2400 | EVAP Leak Detection Pump Control Circuit/Open | General circuit fault, less specific than P2402 | Medium |
| P0440 | EVAP System General Malfunction | May set concurrently if circuit fault affects system operation | Low |
| P0442 | EVAP System Small Leak Detected | Unrelated to P2402 – indicates physical leak | None |
| P0446 | EVAP Vent Control Circuit Malfunction | Different circuit but same system – check shared components | Medium |
| P0455 | EVAP System Large Leak Detected | Unrelated to P2402 – indicates major physical leak | None |
| P0496 | EVAP System High Purge Flow | Different subsystem but may share wiring harness | Low |
Comprehensive Diagnostic Procedure
Preliminary Inspection and Safety
Always begin with a thorough visual inspection. Disconnect the negative battery terminal before working on electrical components. Locate the LDP (typically near the fuel tank or in the engine compartment). Inspect for:
- Physical damage to the LDP or wiring harness
- Corrosion at connectors (green/white deposits)
- Wires chafing against sharp edges or hot components
- Burned or melted insulation near exhaust components
- Proper connector seating (listen for audible click)
Circuit Verification Testing
Using a digital multimeter (DMM) set to DC volts and ohms:
Pin-to-Pin Continuity Check
Disconnect both PCM and LDP connectors. Measure resistance between:
| Test Points | Expected Result | P2402 Failure Indicator |
|---|---|---|
| PCM LDP control pin ↔ LDP control pin | < 5Ω | > 10Ω indicates open circuit |
| LDP control pin ↔ Ground | > 10kΩ | < 100Ω indicates short to ground |
| LDP control pin ↔ Battery + | > 10kΩ | < 100Ω indicates short to power |
| LDP ground pin ↔ Battery – | < 0.5Ω | > 5Ω indicates poor ground |
Component Testing – Leak Detection Pump
Bench test the LDP if circuit testing passes:
- Remove LDP from vehicle
- Apply 12V directly to power terminal
- Ground the ground terminal
- Momentarily apply ground to control terminal
- Pump should activate audibly (click/pump sound)
- Measure coil resistance: 10-50Ω typical
Manufacturer-Specific Variations and Data
| Manufacturer | Common LDP Locations | Typical Repair Times | Special Notes |
|---|---|---|---|
| Ford/Lincoln/Mercury | Right rear wheel well, near fuel tank | 1.2 – 2.0 hours | Prone to corrosion in snow states |
| General Motors | Under vehicle, center near fuel tank | 0.8 – 1.5 hours | Often requires fuel tank shield removal |
| Chrysler/Dodge/Jeep | Left front engine compartment | 0.5 – 1.0 hours | Easy access, common relay failure |
| Toyota/Lexus | Right side engine bay, near strut tower | 1.0 – 1.8 hours | Integrated with VSV, replace as assembly |
| Honda/Acura | Under vehicle, ahead of fuel tank | 1.5 – 2.2 hours | Requires special harness connector tool |
| BMW | Right rear quarter panel | 2.0 – 3.5 hours | Requires ISTA/D for calibration after replacement |
Advanced Technical Data and Specifications
PCM Driver Specifications
The PCM uses a low-side driver (LSD) to control the LDP. Specifications vary by manufacturer:
PCM Low-Side Driver Specifications
| Parameter | Minimum | Typical | Maximum | Unit |
|---|---|---|---|---|
| Output Current Capability | 1.5 | 2.0 | 3.0 | Amps |
| Internal Resistance (On) | 0.05 | 0.1 | 0.2 | Ohms |
| Leakage Current (Off) | – | 1 | 10 | μA |
| Response Time | – | 100 | 500 | μs |
| Short Circuit Protection | 3.5 | 5.0 | 7.0 | Amps |
When the PCM detects a circuit high condition (P2402), it typically disables the driver to prevent damage. This creates a permanent open circuit until the fault is cleared.
