B: Coolant Temperature Reads Erroneously

B1 VERIFY POWER AT FUSE PANEL - LOAD SIDE


^ Using Rotunda Digital Volt-Ohmmeter 014-00407 or equivalent verify system voltage at load side of warning indicator fuse.


^ Is system voltage present at load side of fuse?


Yes

GO to B3


No

GO to B2.



B2 VERIFY POWER AT FUSE PANEL - FEED SIDE


^ Using Rotunda Digital Volt-Ohmmeter 014-00407 or equivalent verify system voltage at feed side of warning indicator fuse.


^ Is system voltage present at feed side of fuse?


Yes

REPLACE fuse.


No

SERVICE wiring to fuse panel.



B3 VERIFY POWER AT INSTRUMENT CLUSTER


^ Partially remove cluster from instrument panel . Using Rotunda Digital Volt-Ohmmeter 014-00407 or equivalent verify system voltage at cluster connector or gauge terminal.


^ Inspect cluster connector for damage.


^ Is voltage present at cluster connector and gauge terminal?


Yes

GO to B4.


No

SERVICE as required.



B4 VERIFY GROUND CIRCUITRY AT CLUSTER

CAUTION: Before checking the continuity of any circuit, make sure there is no voltage present in the circuit prior to switching the test equipment to the resistance function to avoid damage to equipment. Refer to the test equipment user's manual for additional information.


^ Using Rotunda Digital Volt-Ohmmeter 014-00407 or equivalent check continuity of cluster and gauge ground circuitry.


^ Is ground circuitry good?


Yes


GO to B5.


No


SERVICE as required.



B5 TEST SENDER CIRCUIT AT COLD


^ Insert Rotunda Instrument Gauge System Tester 021-00055 or equivalent Disconnect connector at sender and connect tester to cluster side of connector. Set to 74 ohms.


Does gauge read C?

Yes

GO to B6.


No

GO to B7.



B6 TEST SENDER CIRCUIT AT HOT


^ Set Gauge System Tester to 9.7 ohms.


^ Does gauge read H?


Yes

REPLACE coolant temperature sender.


No

GO to B7.



B7 CHECK SENDING UNIT CIRCUIT WIRING



CAUTION: Before checking the continuity of any circuit, make sure there is no voltage present in the circuit prior to switching the test equipment and to the resistance function to avoid damage to equipment. Refer to the test equipment user's manual for additional information.


^ Using Rotunda Digital Volt-Ohmmeter 014-00407 or equivalent check sending unit circuit wiring and instrument cluster printed circuit for shorts or opens by physically flexing the wiring and observing continuity. The continuity reading should not fluctuate.


^ Are wiring and flex circuit OK?


Yes

REPLACE gauge.


No

Aerostar: SERVICE wiring or REPLACE the instrument cluster.

Ranger/Explorer: SERVICE wiring or replace instrument cluster printed circuit.