TEST C - REFERENCE VOLTAGE
Note. Perform this test when a check for VREF signal has failed in sensor input TESTS (DA-DR), or if directed here by TESTS A or QA.
Note. This TEST is intended to diagnose only the ECA, SIG RTN and VREF circuits.
2.9L PFI (Aerostar) Reference Voltage Circuits. Scheme 7
Reference Voltage Ckts All Except 2.9L PFI (Aerostar). Scheme 8
| Test Pin No. | Wire Color |
|---|---|
| Pin 26 (Car Models) | Orange/White |
| Pin 46 (Car Models) | Light Green/Yellow |
REFERENCE VOLTAGE TEST PIN IDENTIFICATION
1) Check Battery Power Circuit Turn key off, wait 10 seconds. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Install breakout box, leaving ECA connected. Turn key on, leaving engine off. Set DVOM on 20-volt scale and measure voltage between test pin No. 37 and SIG RTN/PWR GND circuit in the Self-Test connector. If reading is less than 10.5 volts, reconnect sensor (if applicable) and go to TEST B, step 1. If reading is 10.5 volts or more, go to next step.
2) Check VREF Voltage With breakout box installed and ECA connected, turn key on, leaving engine off. Set DVOM on 20-volt scale and measure voltage between test pins No. 26 and 46 at the breakout box. If reading is 6 volts or more, go to step 4. If reading is 4 volts or less, go to step 5. If reading is between 4 and 6 volts, go to next step.
3) Check VREF & SIG RTN Circuit Continuity With breakout box installed and ECA disconnected, turn key off. If directed here by a sensor test, ensure that sensor is disconnected. Set DVOM on 200-ohm scale. Measure resistance between test pin No. 26 and VREF circuit terminal at the vehicle harness connector of the applicable sensor. Measure resistance between test pin No. 46 and SIG RTN circuit terminal at the vehicle harness connector of the applicable sensor. If both readings are less than 5 ohms, VREF voltage is okay. Remove breakout box, reconnect components and sensor, repeat QUICK TEST. Connect all sensors and repeat QUICK TEST. If any reading is 5 ohms or more, repair open in VREF or SIG RTN circuit. Remove breakout box, reconnect components and repeat QUICK TEST.
4) Check For Excess VREF Circuit Voltage Turn key off and wait 10 seconds. With breakout box installed, disconnect ECA and Scan tool or STAR tester (if applicable). Turn key on, leaving engine off. Set DVOM on 20-volt scale and measure voltage between test pin No. 26 and battery ground. If reading is less than 0.5 volt, replace ECA, remove breakout box, reconnect components and repeat QUICK TEST. If reading is 0.5 volt or more, repair short to battery power in EEC vehicle harness. Remove breakout box, reconnect components and repeat QUICK TEST. Replace ECA if fault still occurs.
5) Check For Shorted TPS Sensor Turn key off and wait for 10 seconds. With breakout box installed and ECA connected, disconnect Throttle Position Sensor (TPS) from vehicle harness. Turn key on, leaving engine off. Set DVOM on 20-volt scale and measure voltage between test pins No. 26 and 46. If reading is 4 volts or more, replace TPS, remove breakout box, reconnect components and repeat QUICK TEST. If voltage is less than 4 volts on models with EVP/PFE sensor, go to next step. If reading is less than 4 volts on all other models, go to step 7.
6) Check For Shorted EVP/PFE Sensor Turn key off and wait 10 seconds. With breakout box installed and ECA connected, disconnect the EVP/PFE sensor. Turn key on, leaving engine off. Set DVOM on 20-volt scale. Measure voltage between test pins No. 26 and 46. If reading is 4 volts or more, replace EVP/PFE sensor and repeat QUICK TEST. If reading is less than 4 volts, go to next step.
7) Check For Shorted MAP/BP Sensor If vehicle is not equipped with a MAP/BP sensor, go to step 10. Turn key off and wait 10 seconds. With breakout box installed and ECA connected, disconnect TPS, EVP/PFE (if equipped) and MAP/BP sensor. Set DVOM on 20-volt scale. With KOEO, measure voltage between test pins No. 26 and 46. If reading is 4 volts or more, replace MAP/BP sensor, remove breakout box, reconnect components and repeat QUICK TEST. If reading is less than 4 volts, go to step 10.
8) Check For Shorted VAF Sensor Turn key off and wait 10 seconds. With breakout box installed and ECA connected, disconnect MAP/BP, TP, and EVP/PFE sensors. Disconnect VAF sensor. Set DVOM on 20-volt scale. With KOEO, measure voltage between test pins No. 26 and 46. If reading is 4 volts or more, replace VAF sensor, remove breakout box, reconnect components and repeat QUICK TEST. If reading is less than 4 volts, go to step 10.
9) Check For Shorted (Models w/ 4EAT Transmission) With key off, disconnect the TPS, MAP/BP, and EVP/PFE sensors (if equipped). Install the breakout box and connect ECA. Disconnect both 4EAT module connectors. With KOEO, set DVOM on 20-volt scale. Measure voltage between test pins No. 26 and 46. If reading is less than 4.0 volts, go to next step. If reading is greater than 4.0 volts, remove breakout box, reconnect all components except 4EAT module and check for short in 4EAT system.
10) Check VREF Circuit For Short to Ground With breakout box installed and ECA disconnected, turn key off and wait 10 seconds. Disconnect TPS, MAP/BP, EVP/PFE, and VAF sensor (if equipped). Set DVOM on 200-ohm scale. Measure resistance between test pin No. 26 and test pins No. 20, 40, 46, and 60. If any resistance is less than 5 ohms, repair short to ground, connect all sensors and repeat QUICK TEST. If original problem still occurs, replace ECA and repeat QUICK TEST. If reading is 5 ohms or more, connect sensors, replace ECA and repeat QUICK TEST.