Test C: Oil Pressure Gauge Inaccurate

NOTE: Ensure engine oil is at proper level and oil pressure switch connector is securely connected. Momentary drop in oil pressure is normal during hard breaking.

Start engine and observe oil pressure gauge. If oil pressure gauge does not indicate "L" (low) or below, go to next step. If oil pressure gauge indicates "L" (low) or below, go to step 5 .
Turn ignition switch to LOCK position. Turn ignition switch to RUN position and observe oil pressure gauge. If oil pressure gauge shows oil pressure, go to next step. If oil pressure gauge does not show oil pressure, system is okay at this time.
Turn ignition switch to LOCK position. Remove instrument cluster. See INSTRUMENT CLUSTER under REMOVAL & INSTALLATION. Turn ignition switch to RUN position. Measure resistance between ground and instrument cluster White 16-pin harness connector C286 terminal No. 12 (Dark Green/White wire). See Fig 1 . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, replace oil pressure gauge and recheck system operation. See GAUGES under REMOVAL & INSTALLATION.

Fig 1: Identifying Instrument Cluster White 16-Pin Harness Connector C286 Terminals
Courtesy of FORD MOTOR CO.
Turn ignition switch to LOCK position. Disconnect oil pressure switch harness connector C175. Measure resistance between ground and instrument cluster White 16-pin connector C286 terminal No. 12 (Dark Green/White wire). If resistance is more than 10 k/ohms, replace oil pressure switch and recheck system operation. If resistance 10 k/ohms or less, repair short to ground in Dark Green/White wire between instrument cluster connector and oil pressure switch harness connector. Recheck system operation.
Turn ignition switch to LOCK position. Disconnect oil pressure switch harness connector C175. Turn ignition switch to RUN position. Connect a fused jumper wire between ground and oil pressure switch harness connector C175 Dark Green/White wire terminal. Observe oil pressure gauge. If oil pressure gauge does not indicate in normal range, go to next step. If oil pressure gauge indicates in normal range, replace oil pressure switch. Recheck system operation.
Turn ignition switch to LOCK position. Disconnect instrument cluster White 16-pin harness connector C286. Measure resistance of Dark Green/White wire between instrument cluster White harness connector C286 terminal No. 12 and oil pressure switch harness connector. See Fig 1 . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Dark Green/White wire between instrument cluster connector and oil pressure switch. Recheck system operation.
Measure resistance between instrument cluster printed circuit at White 16-pin connector terminal No. 12 (component side) and oil pressure gauge terminal "S" clip. If resistance is less than 5 ohms, replace oil pressure gauge. Recheck system operation. See GAUGES under REMOVAL & INSTALLATION. If resistance is 5 ohms or more, replace instrument cluster printed circuit. See PRINTED CIRCUIT under REMOVAL & INSTALLATION. Recheck system operation.