B: Coolant Temperature Reads Inaccurately
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 11.
^ 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 11.
^ Is system voltage present at feed side of fuse?
Yes
REPLACE fuse. RETEST system.
No
SERVICE wiring to fuse panel. RETEST system.
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 Circuit 640 (R/Y) or gauge terminal.
^ Inspect cluster connector for damage.
^ Is voltage present at cluster connector and gauge terminal?
Yes
GO to B4.
No
SERVICE Circuit 640 (R/Y). RETEST system.
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 Circuit 570 (BK/W).
^ Is the resistance less than 1 ohm?
Yes
GO to B5.
No
SERVICE Circuit 570 (BK/W). RETEST system.
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, Circuit 39 (R/W). 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.