Test C2 - Fuel Pump Circuit (Inertia Switch)

To prevent replacement of good components, be aware that the following non-EEC related areas may be at fault: fuel lines, fuel filters, throttle body, fuel pump or contaminated fuel.

Fig 1: 2.3L MPFI Fuel Pump Schematic

Fig 2: 2.3L, 2.9L & 3.0L MPFI Truck Engines

Fig 3: 2.3L OHC MPFI Fuel Pump Schematic

Fig 4: 4.9L, 5.0L & 7.5L MPFI Truck Engines

1. No Fuel Pressure: Electrical Check  - Install fuel pressure gauge. Cycle key from off to on several times to check if fuel pump runs. DO NOT  crank engine. Pump should operate each time key is on. If pump runs as indicated, check fuel pump for problems. If pump does not run as indicated, go to next step.
2. Checking For VPWR to ECA  - Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Install breakout box and reconnect ECA. With KOEO, set DVOM on 20-volt scale and measure voltage between Test Pins No. 37 and 40, and between Test Pins No. 57 and 60. If either reading is less than 10.5 volts, go to TEST A2  , step 1). If both readings are 10.5 volts or more, go to next step.
3. Checking Inertia Switch Resistance  - Turn key off and wait 10 seconds. Leave breakout box installed and ECA connected. Locate and disconnect fuel pump inertia switch. Set DVOM on 200-ohm scale and measure switch resistance. If reading is 5 ohms or more, reset or replace inertia switch. Repeat QUICK TEST  . If reading is less than 5 ohms, reconnect inertia switch and go to next step.
4. Check Voltage to Pump(s)  - With KOEO, breakout box installed and ECA connected. Locate fuel pump relay. Set DVOM on 20-volt scale. Measure voltage between chassis ground and power-to-pump circuit at fuel pump relay while cranking engine. If reading is less than 8 volts, go to next step. If reading is 8 volts or more, check the following: Open in power-to-pump circuit, open in pump and open in ground circuit.
5. Checking Battery Voltage to Fuel Pump Relay  - Turn key on, leaving engine off. Leave breakout box installed and ECA connected, locate fuel pump relay. Set DVOM on 20-volt scale. Measure voltage between chassis ground and V BATT circuit at fuel pump relay. If reading is less than 10.5 volts, repair open in BATT+ circuit between fuel pump relay and battery positive post. Repeat QUICK TEST  . If reading is 10.5 volts or greater, go to next step.
6. Checking VPWR to Fuel Pump Relay  - Turn key on, leaving engine off. Leave breakout box installed and ECA connected. Locate fuel pump relay. Set DVOM on 20-volt scale. Measure voltage between chassis ground and VPWR circuit at fuel pump relay (ignition start/run circuit on 1.9L and 2.3L HSC engines). If reading is 10.5 volts or more, go to next step. If reading is less than 10.5 volts, ensure inertia switch is on. If inertia switch will not reset, replace switch. If switch is okay, repair open in VPWR circuit between EEC power relay and fuel pump relay (Ignition switch Start/Run circuit and fuel pump relay on 1.9L and 2.3L HSC engines). Repeat QUICK TEST  .
7. Checking Fuel Pump Circuit Continuity  - Turn key off and wait 10 seconds. Leave breakout box installed and ECA connected. With DVOM on 200-ohm scale, measure resistance between fuel pump circuit at pump relay and Test Pin No. 22 at breakout box. If reading is 5 ohms or more, repair open in fuel pump circuit. Repeat QUICK TEST  . If reading is less than 5 ohms, go to next step.
8. Checking For Short to Power  - Disconnect ECA and fuel pump relay. With key on, and breakout box installed, set DVOM on 20-volt scale. Measure voltage between Test Pin No. 22 and battery negative terminal. If voltage is less than one volt, go to next step. If voltage is more than one volt, repair short circuit. Reconnect ECA and attempt to start vehicle. If vehicle fails to start, replace ECA. Rerun QUICK TEST  .
9. Checking For Shorts to Ground  - Turn key off. Leave breakout box installed and disconnect ECA. Disconnect fuel pump relay. With DVOM on 200K-ohm scale, measure resistance between Test Pin No. 22 and Test Pins No. 40 and 60. If reading is less than 10K ohms, repair short in fuel pump circuit. Repeat QUICK TEST  . If reading is 10K ohms or more, go to next step.
10. Checking Voltage at Power-to-Pump Circuit  - Leave breakout box installed and ECA disconnected. Install a jumper wire between Test Pin No. 22 and Test Pins No. 40 or 60. Set DVOM on 20-volt scale. With KOEO, measure voltage between chassis ground and power-to-pump circuit at fuel pump relay. If reading is 10.5 volts or more, replace ECA and repeat QUICK TEST  . If reading is less than 10.5 volts, replace fuel pump relay. Connect ECA and repeat QUICK TEST.
11. Code 95: Check Inertia Switch  - A KOEO code 95 indicates that one of the following has occurred:
    • Open circuit in or between ECA and fuel pump.
    • Bad ground connection at fuel pump.
    • Circuit shorted to power.
    • Fuel pump relay contacts always closed.
    Turn key off and wait 10 seconds. Locate and disconnect inertia switch. Set DVOM on 200-ohm scale. Measure resistance of inertia switch. If resistance is less than 5 ohms reconnect inertia switch and go to next step. If resistance is more than 5 ohms, replace or reset inertia switch and rerun QUICK TEST  .
12. Verifying Fuel Pump is Off  - With key off, listen for fuel pump noise. If fuel pump is off, go to step 14). If fuel pump is on, go to next step.
13. Fuel Pump Relay Check  - Turn key off. Remove fuel pump relay. If fuel pump turns off, replace fuel pump relay. Repeat QUICK TEST  . If fuel pump does not turn off, repair short to power-to-pump circuit.
14. Checking Continuity of Fuel Pump Monitor (FPM) Circuit  - Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Install breakout box and leave ECA disconnected. Disconnect fuel pump relay. Set DVOM on 200-ohm scale and measure resistance between Test Pin No. 8 (No. 19 on 5.0L MA SEFI engines) at the breakout box and power-to-pump circuit at the fuel pump relay harness. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open circuit and rerun QUICK TEST  .
15. Checking Continuity Between FPM Circuit and Ground  - Turn key off. Install breakout box and disconnect ECA. Disconnect fuel pump relay. Set DVOM on 200-ohm scale and measure resistance between Test Pin No. 8 (No. 19 on 5.0L MA SEFI Engines) at the breakout box and battery negative terminal. If resistance is less than 10 ohms, go to next step for 1.9L MPFI engines. On all others, remove test set-up, replace ECA and rerun QUICK TEST  . If resistance is more than 10 ohms, remove test set-up and check the following: Open circuit in fuel pump, poor ground connection at fuel pump, or an open in power-to-pump circuit.
16. Checking Fuel Pump Primary Circuit  - Turn key off and wait 10 seconds. Install breakout box and disconnect ECA. Disconnect fuel pump relay and set DVOM on 200K-ohm scale. Measure resistance between Test Pins No. 22 and 40 at the breakout box. If resistance is greater than 10K ohms, remove test set-up. Replace ECA, and rerun QUICK TEST  . If resistance is less than 10K ohms, remove test set-up. Repair short circuit and rerun QUICK TEST. If resistance is greater than 10K ohms, remove test set-up. Replace ECA and rerun QUICK TEST.
17. Code 96: Checking VBATT to Fuel Pump Relay  - Service code 96 indicates that when the fuel pump relay is activated, no power is supplied to pump. Turn key off and wait 10 seconds. Locate fuel pump relay. With the DVOM on 20-volt scale, measure voltage between VBATT circuit at fuel pump relay and battery negative. If voltage is greater than 10.5 volts, go to next step. If voltage is less than 10.5 volts, repair open circuit and rerun QUICK TEST  .
18. Verifying Fuel Pump Operation  - With key off, set DVOM on 20-volt scale. Connect DVOM between pump power circuit at relay and battery negative. Check voltage while turning key on (one second) and off (5 seconds). Cycle at least 5 times. If meter registers greater than 10.5 volts for approximately one second after key is turned off, replace ECA and rerun QUICK TEST  . If voltage is not to specification, inspect relay connector and replace fuel pump relay.
19. Checking Continuity of Power-to-Pump Circuit  - Turn key off and disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Install breakout box and leave ECA disconnected. With DVOM on 200-ohm scale, measure resistance between Test Pin No. 8 (at breakout box) and Power-to-Pump circuit at relay harness connector. If resistance is less than 5 ohms, remove test set-up, replace ECA, and rerun QUICK TEST  . If resistance is more than 5 ohms, repair open circuit between FPM connecting splice and relay. Rerun QUICK TEST.
20. Continuous Code 95: Checking EEC-IV Harness  - A continuous code 95 indicates that one of the following conditions has occurred intermittently: open circuit between ECA pin No. 8 (No. 19 on 5.0L MA SEFI) and pump. Poor ground circuit at pump. Start engine and perform CONTINUOUS MONITOR (WIGGLE) TEST  on harness assembly to fuel pump, and to pump ground circuit harness. Lightly tap inertia switch and pump to simulate road shock. Check for engine miss or stumble while performing test. With key off, check harness connectors for corrosion or damage. If no fault is found, go to next step. Isolate and repair any faults that are found, clear memory code 95 and rerun QUICK TEST  .
21. Checking FPM Circuit  - Turn key off. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Install breakout box and leave ECA disconnected. With KOEO, connect a test light between Test Pins No. 8 (No. 19 on 5.0L MA SEFI) and 37. With test light lit, perform CONTINUOUS MONITOR (WIGGLE) TEST  on FPM circuit between pump and monitor. Light should go out if fault is found during WIGGLE TEST. Isolate and repair any found faults, remove test set-up and rerun QUICK TEST  . If no faults are found, fault cannot be duplicated at this time.
22. Continuous Code 96: Check For Code 87  - If code 87 is also present with code 96, go to step 24). If code 87 is not displayed, go to next
23. Checking EEC-IV Harness  - A continuous code 96 without an accompanying code 87 indicates one of the following occurred during vehicle operation: An open in the VBATT circuit between the battery positive and the fuel pump relay, relay contacts opened or open between FPM circuit and pump power circuit. With engine running, attempt to cause a miss or stumble while performing CONTINUOUS MONITOR (WIGGLE) TEST  on pump harness and connectors. With engine off, inspect all connectors for damage or corrosion. If a fault is found, isolate and repair it. Rerun QUICK TEST  . If no fault is found on 1.9L MPFI engines, go to next step. If no fault is found on all other models, fault may not be duplicated at this time; code 96 testing is complete.
24. Continuous Code 87: Checking EEC-IV Harness  - A continuous code 87 indicates one of the following intermittent conditions has occurred: An open in the VPWR circuit between the EEC power relay and the fuel pump relay, open coil in fuel pump relay or open in fuel pump circuit. With engine running, attempt to cause a miss or stumble while performing CONTINUOUS MONITOR (WIGGLE) TEST  on VPWR circuit between EEC power relay and fuel pump relay. connectors. With engine off, inspect ECA 60-pin connector for damage or corrosion. If a fault is found, isolate and repair it. Rerun QUICK TEST  . If no fault is found, fault may not be duplicated at this time.