Ford 2003 Mustang Workshop Manual page 3873

Pinpoint Tests
CAUTION: Before removing and installing the 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), battery junction box
(BJB) or any connectors. Damage will result to the connector receptacle if the probe being
used is too large.
CAUTION: Electronic modules are sensitive to static electrical charges. 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.
NOTE: 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)
CAUTION: Use the correct probe adapter(s) when making measurements. Failure to
use the correct probe adapter(s) may damage the connector.
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 cirucit(s) in
question. TEST the system