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 directed by QUICK TEST . This CIRCUIT TEST is intended to diagnose the following:

MAF sensor.
Wiring harness circuits (VPWR, PWR GND, MAF SIG and MAF RTN).
Powertrain Control Module (PCM).

To prevent replacement of good components, be aware the following non-EEC related areas may be cause of problem:

Air cleaner element.
Inlet air duct.
Throttle body.

Fig 1: MAF Sensor Circuits & Connector Terminal ID (Ranger)

NOTE: DTC P1101 may be caused by low battery or by use of a garage exhaust ventilation system. Ensure vehicle is vented to outside atmosphere before repeating QUICK TEST .

1) DTC P1101: MAF Output Voltage

DTC P1101, retrieved during KOEO self-test, indicates voltage exceeded .2-volt test range. DTC P1101, retrieved during KOER self-test, indicates voltage is not within .34-1.96 volts operating range. Possible causes for this fault are:

Air leak before or after MAF sensor.
Faulty MAF sensor.
Faulty MAF sensor wiring harness connector.
Open PWR GND or MAF RTN circuit.
Faulty PCM.

Turn ignition off. Disconnect PCM 104-pin connector and inspect for damage. Repair as necessary. Install Breakout Box (014-00950). Leave PCM connected to breakout box. With scan tester connected, turn ignition on. Measure voltage between test pin No. 88 (MAF SIG) and test pins No. 24 and 103 (PWR GND). If voltage is greater than 0.2 volt, go to step 12). If voltage is 0.2 volt or less, go to step 9).

2) Continuous Memory DTC P1100: Check MAF Circuit Intermittent Voltage Input

DTC P1100 indicates voltage went out of range (0.39-3.90 volts) sometime during previous 40 warm-up cycles. Possible causes for this fault are:

Faulty MAF sensor.
Faulty MAF sensor wiring harness or connector.

Start engine and allow to idle. If engine does not idle smoothly, repair cause of rough idle condition before continuing. With scan tester connected, raise engine speed to 1500 RPM for 5 seconds, and return to idle. Access MAF PID. While observing PID, tap on sensor to simulate road shock. Wiggle sensor connector. If MAF PID voltage stays within 0.39-3.90 volt range, go to next step. If volt range is not as specified, check MAF sensor and connector. Repair or replace as necessary.

3) Check MAF Sensor Circuit Integrity

Turn ignition off. Disconnect PCM 104-pin connector and inspect for damage. Repair as necessary. Install Breakout Box (014-00950). Connect PCM to breakout box. Turn ignition on. Connect voltmeter between test pin No. 36 (MAF RTN) and No. 88 (MAF SIG). While observing voltmeter, wiggle and bend wiring harness between sensor and dash panel. Wiggle and bend wiring harness between dash panel and PCM. If voltage reading goes out of normal range (0.39-3.90 volts), isolate fault and repair as necessary. Reset KAM and repeat QUICK TEST . If voltage does not go out of normal range, fault cannot be duplicated or identified at this time. Testing is complete.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 3) to step 6). No test procedures have been omitted.

6) Continuous Memory & KOER DTC P0102: Check MAF Low Input Signal To PCM

DTC P0102 indicates MAF signal was less than 0.39 volt sometime during normal engine operation. Possible causes for this fault are:

Open or closed MAF circuit.
MAF circuit shorted to ground.
Faulty MAF sensor or connector.
Faulty TP sensor.

Ensure air induction system is okay. Repair if necessary. Start engine and allow to idle. If engine does not idle smoothly, repair cause of rough idle condition before continuing. With scan tester connected, raise engine speed to 1500 RPM and return to idle. Access MAF PID. If MAF PID is less than 0.39 volt, go to next step. If MAF PID is 0.6-1.0 volt, go to step 15). For all other MAF PID readings, go to step 2).

7) Check VPWR Circuit Voltage

Turn ignition off. Disconnect MAF sensor. Turn ignition on. Measure voltage between VPWR terminal of MAF sensor wiring harness connector and negative battery terminal. 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 .

8) Check Continuity Of VPWR Circuit

Turn ignition off. Disconnect PCM 104-pin connector and inspect for damage. Repair as necessary. Install Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between VPWR terminal of MAF sensor wiring harness connector and test pins No. 71 and 97 (VPWR) at breakout box. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in VPWR circuit and repeat QUICK TEST .

9) Check MAF Circuit For Short To Ground & MAF RTN Circuit

Leave ignition off and MAF disconnected. Disconnect scan tester from DLC (if applicable). Measure resistance between test pin No. 88 (MAF SIG) and test pins No. 24, 36 (MAF RTN), and 103 (PWR GND) at breakout box. If resistance is 10,000 ohms or more, reconnect scan tester and go to next step. If resistance is less than 10,000 ohms, repair circuit short to ground and repeat QUICK TEST .

10) Check Continuity Of MAF SIG Circuit

Leave ignition off and MAF disconnected. Measure resistance between MAF terminal of MAF sensor wiring harness connector and test pin No. 88 (MAF SIG) at breakout box. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit in MAF SIG circuit and repeat QUICK TEST .

11) Check PWR GND Circuit To MAF Sensor

Leave ignition off and MAF disconnected. Turn ignition on. Measure voltage between VPWR and PWR GND terminal of MAF sensor wiring harness connector. If voltage is less than 10.5 volts, go to next step. If voltage is 10.5 volts or more, go to step 13).

12) Check PWR GND Circuit Continuity

Leave ignition off and MAF sensor disconnected. Disconnect scan tester from DLC (if applicable). Measure resistance between PWR GND terminal of MAF sensor wiring harness connector and negative battery terminal. If resistance is less than 10 ohms, go to next step. If resistance is 10 ohms or more, repair open in PWR GND circuit and repeat QUICK TEST .

13) Check MAF RTN Circuit Continuity

Leave ignition off and MAF sensor disconnected. Measure resistance between MAF RTN terminal of MAF sensor wiring harness connector and test pin No. 36 (MAF RTN) at breakout box. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in MAF RTN and repeat QUICK TEST .

14) Check MAF Circuit For Short To Ground In PCM

Leave ignition off and MAF disconnected. Connect PCM to breakout box. Disconnect scan tester from DLC (if applicable). Measure resistance between test pin No. 88 (MAF SIG) and test pins No. 24, 36 (MAF RTN) and 103 (PWR GND) at breakout box. If resistance is 10,000 ohms or more, go to next step. If resistance is less than 10,000 ohms, replace PCM and repeat QUICK TEST .

15) Check MAF Circuit Output

Ensure ignition is off. Reconnect MAF sensor. Connect PCM to breakout box. Start engine and allow to idle. If engine does not idle smoothly, repair cause of rough idle condition before continuing. Measure voltage between test pin No. 88 (MAF SIG) and negative battery cable. If voltage is 0.34-1.96 volts, go to next step. If voltage is not 0.34-1.96 volts, replace MAF sensor and repeat QUICK TEST .

16) Check MAF Circuit Output With Scan Tester

Start engine and allow to idle. Access MAF PID on scan tester. If PID voltage is 0.34-1.96 volts, go to next step. If voltage is not 0.34-1.96 volts, replace MAF sensor and repeat QUICK TEST .

17) Check MAF Circuit Input & Output

Turn ignition off. Leave PCM connected to breakout box. Start engine and allow to idle. Measure voltage between test pin No. 36 (MAF RTN) and No. 88 (MAF SIG) at breakout box. If voltage is 0.34-1.96 volts, replace PCM and repeat QUICK TEST . If voltage is not 0.34-1.96 volts, replace MAF sensor and repeat QUICK TEST .

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 17) to step 20). No test procedures have been omitted.

20) DTC P0103: Check MAF High Input Signal To PCM

DTC P0103 indicates MAF signal was more than 4.70 volts sometime during normal engine operation. Possible causes for this fault are as follows:

Restricted MAF sensor screen.
MAF SIG circuit shorted to VPWR.
Faulty MAF sensor or connector.
Faulty PCM.

Ensure air induction system is okay. Repair if necessary. Start engine and allow to idle. If engine does not idle smoothly, repair cause of rough idle condition before continuing. With scan tester connected, raise engine speed to 1500 RPM and return to idle. Access MAF PID. PID reading should be more than 3.90 volts. Turn ignition off. Disconnect MAF sensor. Start engine and allow to idle. Access MAF PID. If PID voltage reading does not drop to less than 0.39 volt, go to next step. If PID voltage reading does drop to less than 0.39 volt, replace MAF sensor.

21) Check MAF SIG Circuit For Short To Power

Leave ignition off and MAF sensor disconnected. Disconnect PCM 104-pin connector and inspect for damage. Repair as necessary. Install Breakout Box (014-00950), leaving PCM disconnected. Turn ignition on. Measure voltage between test pin No. 88 (MAF SIG) and test pins No. 24 and 103 at breakout box. If voltage is less than 10.5 volts, go to next step. If voltage is 10.5 volts or more, repair MAF SIG circuit short to power.

22) Check MAF SIG Circuit For Short To Power In PCM

Leave ignition off and MAF sensor disconnected. Disconnect scan tester from DLC (if applicable). Measure resistance between test pin No. 88 (MAF SIG) and test pins No. 71 and 97 (VPWR) at breakout box. If resistance is more than 10,000 ohms, replace PCM and repeat QUICK TEST . If resistance is 10,000 ohms or less, repair short in MAF SIG circuit and repeat QUICK TEST .