Express, Savana, G1500, G2500, G3500, 1998-2005

6.5L V8 VIN F Auto 3

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Trouble Code: P1639



5-Volt Reference Circuit Low Input

Possible Causes:



5v VREF circuit is shorted to sensor ground or chassis ground
 
5v VREF circuit, Boost or CKP sensor circuit is shorted to (B+)
 
5v VREF circuit shorted to the Boost sensor signal circuit
 
EGR solenoid valve (and sensor) is damaged or has failed
 
PCM has failed
 

Trouble Code: P1641



MIL Control Circuit Malfunction

Possible Causes:



MIL control circuit is open, shorted to ground or to power (B+)
 
MIL (lamp) is damaged or failed (open circuit or missing)
 
MIL power circuit is open (check GAUGES fuse in fuse block)
 
PCM has failed
 

Trouble Code: P1643



Wait To Start Lamp Control Circuit Malfunction

Possible Causes:



Wait to start lamp control circuit is open, shorted to ground or shorted to power (B+)
 
Wait to start lamp power circuit is open (check GAUGES fuse)
 
Wait to start "bulb" is open or is missing
 
PCM has failed
 

Trouble Code: P1653



EGR Vent Solenoid Control Circuit Malfunction

Possible Causes:



Vent solenoid control circuit is open, shorted to ground or to B+
 
Vent solenoid power circuit is open (check the ENG1 fuse)
 
Vent solenoid is damaged, or the PCM has failed
 

Trouble Code: P1654



Service Throttle Soon Lamp Control Circuit Malfunction

Possible Causes:



STS lamp control circuit is open, shorted to ground or to system power (B+)
 
STS lamp (bulb) is open or missing
 
STS lamp power circuit is open (power is through the IPC)
 
PCM has failed
 

Trouble Code: P1655



EGR Control Solenoid Control Circuit Malfunction

Possible Causes:



EGR solenoid control circuit is open, shorted to ground or to system power (B+)
 
EGR solenoid power circuit is open (check the ENG1 fuse)
 
EGR solenoid is damaged or has failed
 
PCM has failed
 

Trouble Code: P1656



Wastegate Solenoid Control Circuit Malfunction

Possible Causes:



Waste solenoid circuit is open, shorted to ground or to power (B+)
 
Wastegate solenoid power circuit is open (check ENG1 fuse)
 
Wastegate solenoid is damaged or has failed
 
PCM has failed
 

Trouble Code: U1000



Class 2 Communication Malfunction

Possible Causes:



Class 2 circuit is open, shorted to ground or shorted to power
 
PCM ignition power circuit(s) has a high resistance condition
 
PCM main ground circuit(s) has a high resistance condition
 
SDM (module) could be shorted pulling the voltage low
 

Trouble Code: U1016



No Communication With Powertrain Control Module

Possible Causes:



PCM Class 2 circuit is open, shorted to ground or to B+
 
PCM ignition power circuit(s) has a high resistance condition
 
PCM main ground circuit(s) has a high resistance condition
 
PCM (module) may have failed and is pulling the circuit low
 

Trouble Code: U1026



Loss of ATC Class 2 Communication

Possible Causes:



Check for a loose connection at the ATC module
 
Test the main power and ground circuits to the ATC module
 
Check the Class 2 serial data circuit to the ATC module
 
ATC module may have failed
 

Trouble Code: U1041



Loss of Electronic Brake Controller Communication

Possible Causes:



Check for a loose connection at the EBCM (module)
 
Test the main power and ground circuits to the EBCM (module)
 
Check the Class 2 serial data circuit to the EBCM (module)
 
EBCM (module) may have failed
 

Trouble Code: U1048



No Communication With Rear Wheel Steering Control Module

Possible Causes:



RWSCM Class 2 circuit is open, shorted to ground or to B+
 
RWSCM ignition power circuit has a high resistance condition
 
RESCM main ground circuit(s) has a high resistance condition
 
RESCM (module) may have failed and is pulling the circuit low
 

Trouble Code: U1064



No Communication With Body Control Module

Possible Causes:



BCM Class 2 circuit is open, shorted to ground or to B+
 
BCM ignition power circuit has a high resistance condition
 
BCM main ground circuit(s) has a high resistance condition
 
BCM (module) may have failed and is pulling the circuit low
 

Trouble Code: U1088



No Communication With SDM (Restraint Module)

Possible Causes:



SDM Class 2 circuit is open, shorted to ground or to B+
 
SDM ignition power circuit has a high resistance condition
 
SDM main ground circuit(s) has a high resistance condition
 
SDM (module) may have failed and is pulling the circuit low
 

Trouble Code: U1092



Loss of VTD (Pass Lock) Communication

Possible Causes:



Check for a loose connection at the VTD module
 
Test the main power and ground circuits to the VTD module
 
Check the Class 2 serial data circuit to the VTD module
 
VTD module may have failed
 

Trouble Code: U1096



No Communication With Instrument Panel Cluster

Possible Causes:



IPC Class 2 circuit is open, shorted to ground or to B+
 
IPC ignition power circuit has a high resistance condition
 
IPC main ground circuit(s) has a high resistance condition
 
IPC (module) may have failed and is pulling the circuit low
 

Trouble Code: U1097



No Communication With Driver Information Center

Possible Causes:



DIC Class 2 circuit is open, shorted to ground or to B+
 
DIC ignition power circuit has a high resistance condition
 
DIC main ground circuit(s) has a high resistance condition
 
DIC (module) may have failed and is pulling the circuit low
 

Trouble Code: U1151



No Communication With Vehicle Interface Unit

Possible Causes:



VIU Class 2 circuit is open, shorted to ground or to B+
 
VIU ignition power circuit has a high resistance condition
 
VIU main ground circuit(s) has a high resistance condition
 
VIU (module) may have failed and is pulling the circuit low
 

Trouble Code: U1152



No Communication With HVAC Control Module

Possible Causes:



HVAC Class 2 circuit is open, shorted to ground or to B+
 
HVAC ignition power circuit has a high resistance condition
 
HVAC main ground circuit(s) has a high resistance condition
 
HVAC (module) may have failed and is pulling the circuit low
 

Trouble Code: U1193



Loss of Vehicle Immobilizer Module Communications

Possible Causes:



Test the main power and ground circuits to the VIM module for a loose connection
 
Check the Class 2 serial data circuit to the VIM module
 
VTD module may have failed
 

Trouble Code: U1255



Class 2 Communications Malfunction

Possible Causes:



Class 2 circuit is open, shorted to ground or shorted to power
 
PCM ignition power circuit(s) has a high resistance condition
 
PCM main ground circuit(s) has a high resistance condition
 

Trouble Code: U1305



Class 2 Data Link High or Low

Possible Causes:



Class 2 serial data line has either a high or low voltage condition on the circuit, and the module cannot identify the fault
 
One or more modules on Class 2 line has an short to power
 
One or more modules on the Class 2 line has a short to ground
 

 
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