Diagnostic Aids

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

Perform this test when directed by QUICK TEST procedure. This CIRCUIT TEST is intended to diagnose:

Wiring harness circuits (EGRT and SIGRTN).

Fig 1: EGRT Circuits & Connector Terminal ID

EGRT CIRCUIT INFORMATION

Circuit

PCM Pin No.

⁽¹⁾ BOB Pin No.

Wire Color

EGRT

White/Pink

SIGRTN

21 & 29

White/Black

⁽¹⁾	Rotunda Breakout Box (007-00033).

1) Check EGRT Signal To PCM Turn ignition off. Connect scan tester to DLC. Using scan tester, check EGRT sensor voltage. If voltage is less than 4.5 volts, EGRT sensor is okay and testing is complete. If voltage is 4.5 volts or more, go to next step.

2) Check EGRT Sensor Resistance Allow engine to cool. Start engine. Use a thermometer to monitor engine coolant temperature. Warm engine to temperature specifications shown in EGRT SENSOR RESISTANCE SPECIFICATIONS table. Turn ignition off. Disconnect EGRT wiring harness connector. Measure resistance between connector terminals. If resistance is correct, go to next step. If resistance is not correct, replace EGRT sensor.

EGRT SENSOR RESISTANCE SPECIFICATIONS

Coolant Temperature °F (°C)	M Ohms
68-120 (20-49)	2.25-2.55
130-148 (55-65)	1.75-2.25
150-165 (66-74)	1.40-1.75
168-190 (76-88)	1.00-1.40

3) Check EGRT Sensor Start engine and allow to idle until engine is at normal operating temperature. Raise engine speed to 2000 RPM. Check voltage at EGRT sensor wiring harness connector terminals. Apply vacuum to EGR valve. If voltage drops from more than one volt to less than one volt, go to next step. If voltage does not drop as specified, replace EGRT sensor.

4) Check EGRT Circuit Turn ignition off. Install Breakout Box(007-00033), leaving PCM disconnected. Leave EGRT wiring harness connector disconnected. Disconnect in-line connector located on right side of intake plenum. Measure resistance between breakout box test pin No. 25 and EGRT terminal of EGRT in-line connector. Measure resistance between EGRT terminal of EGRT in-line connector and EGRT terminal of EGRT sensor harness connector. Resistance should be 5 ohms or less. Reconnect in-line connector. Measure resistance between breakout box test pin No. 25 and ground. Resistance should be 10,000 ohms or more. If resistance is as specified, go to next step. If resistance is not as specified, repair or replace circuit.

5) Check SIGRTN Circuit Leave ignition off and EGRT wiring harness connector disconnected. Measure resistance between breakout box test pin No. 46 and SIGRTN terminal of in-line connector. Measure resistance between SIGRTN terminal of in-line connector and SIGRTN terminal of EGRT wiring harness connector. If both resistance values are 5 ohms or less, replace PCM. If either resistance value exceeds 5 ohms, repair circuit as necessary.