Ford 2003 Mustang Workshop Manual page 3323

Pinpoint Tests
CAUTION: Before removing and installing the generic electronic module (GEM) or its
connectors, disconnect the battery. Failure to follow this caution will result in the GEM storing
many erroneous DTCs, and it may exhibit erratic operation after installation.
CAUTION: Be careful when probing the central junction box (CJB), or any connectors.
Damage will result to the connector receptacle if the probe or terminal used is too large.
CAUTION: Electronic modules are sensitive to static discharges. If exposed to these
charges, damage may result.
NOTE: If continuous DTCs are recorded and the symptom is not present when carrying out the
pinpoint tests, an intermittent concern may be the cause. Always check for loose connections and
corroded terminals.
Complete the entire pinpoint test related to the symptom before installing a new GEM.
PINPOINT TEST A: NO COMMUNICATION WITH THE GENERIC
ELECTRONIC MODULE (GEM)
A1 CHECK THE GENERIC ELECTRONIC MODULE (GEM)
POWER SUPPLY
Key in OFF position.
Disconnect: Generic Electronic Module (GEM) C201a.
Disconnect: GEM C201b.
Key in ON position.
Using the following table, measure the voltage between the
GEM, harness side and ground.
Connector Pin
C201a 4
C201a 1
C201b 2
C201b 3
Are the voltages greater than 10 volts?
A2 CHECK THE GEM GROUND CIRCUIT 397 (BK/WH) FOR
OPEN
Key in OFF position.
Measure the resistance between the GEM C201b pin 4,
circuit 397 (BK/WH), harness side and ground.
Test Step
Circuit
400 (LB/BK)
1006 (DG/WH)
1001 (WH/YE)
193 (YE/LG)
Result / Action to Take
Yes
GO to A2 .
No
REPAIR the circuit(s) in
question. TEST the system
for normal operation.
Yes
GO to A3 .
No
REPAIR the circuit(s) in
question. TEST the system
for normal operation.