Diagnostic Aids

WARNING: This page is about a different car, the 1995 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.

Perform this test when instructed during QUICK TEST or if directed by other test procedures. This test is used to diagnose the following:

Canister Purge (CANP) solenoid.
Carbon canister.
Leaks in fuel tank, filler cap or vapor hoses.
Wiring harness circuits (CANP SIG, PWR GND, SIG RTN, and VPWR).
Faulty vapor orifice rollover valve.
Faulty Powertrain Control Module (PCM).

Fig 1: Identifying EVAP System Components (Ranger)

Fig 2: CANP Test Circuit Diagram (Ranger)

1) Check CANP Or VMV Solenoid Function

Turn ignition off. Connect scan tester to DLC. Disconnect cruise control wiring harness connector (if equipped). Disconnect CANP solenoid or VMV wiring harness connector. Connect DVOM positive lead to VPWR terminal and negative lead to CANP or VMV terminal of wiring harness connector. Turn ignition on. Activate scan tester Outputs mode. Measure and record voltage reading on DVOM. Turn off scan tester Outputs mode. Measure and record voltage reading on DVOM. Repeat on and off cycle with scan tester. If CANP or VMV voltage is less than 0.2 volt during cycle, go to step 9). If CANP or VMV voltage is 0.2 volt or more, go to next step.

2) Check CANP Or VMV Resistance

Turn ignition off. Leave wiring harness connector disconnected. Measure resistance between connector terminals. If resistance is 30-90 ohms, go to next step. If resistance is not as specified, replace CANP solenoid. Clear PCM memory and repeat QUICK TEST.

3) Check Carbon Canister

Vehicle must have been operated for a period of time equivalent to a drive cycle to purge all fuel vapors. Check for cracks or damage to canister. Repair or replace as necessary. If canister is okay, go to next step.

4) Check EVAP System Vacuum

Remove fuel vapor hose from fuel tank at canister. Attach vacuum pump with gauge to vacuum hose. Using vacuum pump, apply 1.0 in. Hg to fuel vapor hose. If system holds vacuum, go to next step. If system will not hold vacuum, isolate leak and repair as necessary.

5) Check Vacuum Hose

Check vacuum hose between fuel tank and carbon canister for faults. Check for fuel tank damage. Check for damaged orifice rollover valve. Repair or replace as necessary. If no faults are found, go to next step.

6) Check CANP Solenoid Vacuum

Turn ignition off. Ensure CANP solenoid is disconnected. Disconnect vacuum hose from CANP solenoid manifold side. Using a vacuum pump, apply 16 in. Hg to CANP solenoid. If vacuum is held for 20 seconds, release vacuum from solenoid and go to next step. If vacuum is not held for 20 seconds, replace CANP solenoid.

7) Check CANP Solenoid

Turn ignition off. Reconnect CANP solenoid wiring harness connector. Ensure CANP solenoid vacuum hoses are disconnected. Connect scan tester to Data Link Connector (DLC). Using scan tester, access Output Test Mode (OTM). Using vacuum pump, apply 16 in. Hg to CANP solenoid. Turn ignition on. CANP solenoid should open and release vacuum when scan tester output is commanded on. If CANP solenoid functions as specified, check fuel vapor hose for leaks, restrictions or mis-routing. Repair or replace as necessary. If CANP solenoid does not function as specified, replace CANP solenoid.

8) Check Vacuum Hose

Check vacuum hose between CANP solenoid and carbon canister for faults. Repair or replace as necessary. If no faults are found, go to next step.

9) Check Manifold Vacuum To CANP Solenoid

Turn ignition off. Disconnect vacuum hose from CANP solenoid manifold side. Start engine and allow to idle. Check for vacuum at CANP solenoid hose. If vacuum is present, system is functioning correctly and testing is complete. If vacuum is not present, check vacuum circuit for leaks, restrictions or mis-routing. Repair or replace as necessary.

10) Check Vacuum At VMV

Turn ignition off. Ensure VMV solenoid is disconnected. Disconnect vacuum hose from VMV solenoid input port. Start engine and allow to idle. Check for vacuum at open end of vacuum hose. If vacuum is present, reconnect hose and go to next step. If vacuum is not present, check vacuum hose and vacuum source for obstruction.

11) Turn ignition off. Ensure VMV solenoid is disconnected. Disconnect vacuum tree-to-VMV vacuum hose from VMV solenoid input port. Start engine and allow to idle. Check for vacuum at open end of vacuum hose. If vacuum is present, reconnect hose and go to next step. If vacuum is not present, check vacuum hose and vacuum source for obstruction.

12) Turn ignition off. Reconnect VMV solenoid. Using a vacuum pump, apply 16 in. Hg to VMV solenoid fuel vapor to intake manifold port. See Fig 3. Turn ignition on. Note vacuum reading. Release vacuum applied by pump. If vacuum reading drops, exit output test mode and go to next step. If vacuum does not drop, replace VMV solenoid.

Fig 3: VMV Solenoid Vacuum Hose Terminal ID (Ranger)

13) Turn ignition off. Disconnect VMV solenoid. Turn ignition on. Using a vacuum pump, apply 16 in. Hg to VMV solenoid vacuum input port. Note vacuum reading. Turn ignition off. If vacuum reading drops, go to next step. If vacuum does not drop, replace damaged fuel vapor hose.

14) Turn ignition off. Disconnect vacuum hose between carbon canister and VMV solenoid. Plug one end of hose. Using a vacuum pump, apply 16 in. Hg to hose. If vacuum is held for 15 seconds, reconnect hose and go to next step. If vacuum is not held for 15 seconds, replace hose and repeat QUICK TEST.

15) Leave ignition off. Disconnect vacuum hose between carbon canister and fuel tank at carbon canister. Using a vacuum pump, apply 1.0 in. Hg to hose. If vacuum is held, check vacuum hose for obstruction and repair as necessary. If vacuum is not held, go to next step.

16) Leave ignition off. Check vacuum hose between carbon canister and fuel tank. Repair hose if damaged or worn. Check fuel tank for damage. Check rollover valve. Repair faulty components as necessary. If no faults are found and symptom is still present, go to appropriate TESTS W/O CODES article.

TESTS W/O CODES - EEC-V (for Ranger)

17) DTC P0443: Check VPWR Circuit Voltage

Disconnect CANP or VMV solenoid wiring harness connector. Turn ignition on. Measure voltage between VPWR terminal of solenoid wiring harness connector and battery ground. If voltage is 10.5 volts or more, go to next step. If voltage is less than 10.5 volts, repair open in VPWR circuit and repeat QUICK TEST.

18) Check CANP Or VMV Resistance

Turn ignition off. Leave solenoid disconnected. Measure resistance between solenoid terminals. If resistance is 30-90 ohms, go to next step. If resistance is not as specified, replace CANP solenoid. Clear PCM memory and repeat QUICK TEST.

19) Check CANP SIG Circuit Continuity

Turn ignition off. Disconnect PCM wiring harness connector. Inspect pins for damage and repair as necessary. Install EEC-V Breakout Box (014-000950), leaving PCM disconnected. On Ranger, measure resistance between test pin No. 67 (CANP) and CANP terminal of CANP solenoid wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in CANP SIG circuit. Clear PCM memory and repeat QUICK TEST.

20) Check CANP SIG Circuit For Short To Ground

Leave ignition off. Disconnect scan tester from DLC. On Ranger, measure resistance between test pin No. 67 and test pins No. 24, 91 and 103. If each resistance reading is more than 10,000 ohms, go to next step. If any resistance is 10,000 ohms or less, repair short to ground in CANP or VMV circuit. Clear PCM memory and repeat QUICK TEST.

21) Check CANP SIG Circuit For Short To VPWR

Leave ignition off and solenoid disconnected. On Ranger, measure resistance between test pin No. 67 and test pins No. 71 and 91. If each resistance is more than 10,000 ohms, replace PCM and repeat QUICK TEST. If any resistance is 10,000 ohms or less, repair CANP SIG circuit short to VPWR. Clear PCM memory and repeat QUICK TEST.

22) Continuous Memory DTC P0443: Check CANP Or VMV Circuit For Intermittent Failure

Repeat QUICK TEST. If Continuous Memory DTC P0443 is still present, go to next step. If Continuous Memory DTC P0443 is not present, return to step 17).

23) Wiggle Test Solenoid & Harness

Turn ignition off. Disconnect PCM wiring harness connector. Inspect pins for damage and repair as necessary. Install EEC-V Breakout Box (014-000950), leaving PCM disconnected. On Ranger, measure resistance between test pin No. 67 and test pins No. 71 and 91. Observe DVOM for indication of fault while shaking and bending solenoid wiring harness and connector. A fault will be indicated by resistance measurement of less than 30 ohms or more than 90 ohms. Tap lightly on CANP solenoid to simulate road shock. If fault is indicated, isolate and repair as necessary. If no fault is indicated, go to CIRCUIT TEST Z.