Avalanche, Sierra, Silverado, C&K Series, 1999-2005

6.0L V8 VIN U Auto 5

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Trouble Code: P1631



Theft Deterrent - Start Enable Signal Not Correct

Possible Causes:



Refer to Diagnostic System Check for Theft Deterrent Module
 
Perform the Powertrain Onboard Diagnostic System Check
 
TSB 77-65-31 contains a repair procedure for this code
 

Trouble Code: P1635



5-Volt Reference 1 Circuit Malfunction

Possible Causes:



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

Trouble Code: P1637



Generator 'L' Terminal Circuit Malfunction

Possible Causes:



A Scan Tool should display Inactive for the 'L' Terminal and 10-40% for the 'F' Terminal with the ignition "on". With the engine running, the display should indicate the 'L' Terminal is Active and the 'F' Terminal is higher than 5% on the tool display.
 
Generator 'L terminal circuit shorted to ground or to power (B+)
 
Generator 'F' terminal circuit is open or shorted to ground
 
Generator is damaged or has failed or the PCM has failed
 

Trouble Code: P1638



Generator 'F' Terminal Circuit Malfunction

Possible Causes:



Generator connector is damaged or has high resistance
 
Generator field duty cycle signal circuit is open or shorted
 
Generator is damaged or has failed
 
PCM has failed
 

Trouble Code: P1639



5-Volt Reference 2 Circuit Malfunction

Possible Causes:



5v VREF circuit is shorted to sensor ground or chassis ground
 
5v VREF circuit, FTP or TP sensor circuit is shorted to (B+)
 
5v VREF circuit shorted to FTP or TP sensor signal circuit
 
FTP sensor or TP sensor is damaged or PCM has failed
 

Trouble Code: P1680



Powertrain Control Module Internal Malfunction

Possible Causes:



Clear the codes and then recheck for this trouble code. If the same code resets, the PCM is damaged and must be replaced (and the new PCM must be programmed) to repair this code.
 

Trouble Code: P1681



Powertrain Control Module Internal Malfunction

Possible Causes:



Clear the codes and then recheck for this trouble code. If the same code resets, the PCM is damaged and must be replaced (and the new PCM must be programmed) to repair this code.
 

Trouble Code: P1683



Powertrain Control Module Internal Malfunction

Possible Causes:



Clear the codes and then recheck for this trouble code. If the same code resets, the PCM is damaged and must be replaced (and the new PCM must be programmed) to repair this code.
 

Trouble Code: P1810



TFP Valve Position Switch Assembly (4L60-E, 4L65-E, 4L80-E)

Possible Causes:



TFP valve position switch signal circuit is open, grounded or shorted to another signal
 
TFP valve position switch is damaged or has failed
 
This code can set during fluid refilling. After refilling the fluid, cycle the key "off", then idle the engine for 20 seconds. Turn the key "off" and allow the PCM to power down.
 
This code can set due to low pump pressure or due to a stuck pressure regulator.
 
This code can set due to a rolled forward clutch piston seal. It may allow the PCM to see a 2.08:1 ratio (reverse) when the manual valve position is actually indicated in D4.
 
PCM has failed
 

Trouble Code: P1860



TCM PWM Solenoid Circuit Malfunction (4L60-E, 4L65-E, 4L80-E)

Possible Causes:



TCC solenoid control circuit is open or shorted to ground
 
TCC solenoid control circuit is shorted to system power (B+)
 
TCC solenoid power circuit is open (test TRANS or IGN fuse)
 
TCC solenoid is damaged or has failed
 
PCM has failed
 

Trouble Code: P1870



Transmission Component Slipping (4L60-E, 4L65-E, 4L80-E)

Possible Causes:



1-2 shift solenoid valve has sediment, damage or leaking seals
 
2-3 shift solenoid valve has sediment, damage or leaking seals
 
3-2 shift solenoid valve has sediment, damage or leaking seals
 
Valve body regulator apply valve stuck or regulator is scored
 
Torque converter front stator shaft bushing is worn, the stator roller clutch is not holding or it has external damage/leaks
 
Converter clutch valve is stuck or it is installed backwards
 
Converter clutch valve retaining ring is not positioned properly
 
Converter clutch outer valve spring is cocked
 
Pump to case gasket is not positioned properly
 
Orifice cup plugs are restricted or damaged
 
Over-tightened, or unevenly tightened pump body to cover bolts
 
TSB 02-07-30-001 contains a repair procedure for this code
 

Trouble Code: P1875



4WD Low Switch Circuit Fault (4L60-E, 4L65-E, 4L80-E)

Possible Causes:



4WD low switch signal circuit is open, shorted to ground or B+
 
4WD low switch is damaged or has failed
 
PCM has failed
 

Trouble Code: P2066



Secondary Fuel Sensor Signal Range/Performance

Possible Causes:



Perform the I/P Cluster Diagnostic System Check
 
Check the fuel tank for signs of foreign material (i.e., ice)
 
Fuel level sender is malfunctioning (check the fuel strainer to determine if it is interfering with the sender float arm - sticking)
 
Fuel level sensor is damaged or it has failed
 

Trouble Code: P2067



Secondary Fuel Level Sensor Circuit Low Input

Possible Causes:



Perform the I/P Cluster Diagnostic System Check
 
Fuel level sensor connector is damaged or shorted
 
Fuel level sensor signal circuit is shorted to ground
 
Fuel level sensor is damaged or it has failed
 

Trouble Code: P2068



Secondary Fuel Level Sensor Circuit High Input

Possible Causes:



Perform the I/P Cluster Diagnostic System Check
 
Fuel level sensor connector is damaged, open or shorted
 
Fuel level sensor signal circuit is open or shorted to power
 
Fuel level sensor is damaged or it has failed
 

Trouble Code: P2108



Throttle Actuator Control Module Internal Data Test Failed

Possible Causes:



TAC module is damaged or it has failed
 

Trouble Code: P2120



Accelerator Pedal Position Sensor 1 Signal Performance

Possible Causes:



APP sensor connector is damaged, open or shorted
 
APP1 sensor signal circuit is open or shorted to ground
 
APP1 sensor signal circuit is shorted to APP sensor 2 circuit
 
APP1 sensor signal circuit is open or shorted to VREF (5v)
 
APP sensor is damaged or it has failed
 
TAC module is damaged or it has failed
 

Trouble Code: P2121



Accelerator Pedal Position Sensor 1-2 Correlation Malfunction

Possible Causes:



APP sensor connector is damaged, open or shorted
 
APP1 sensor low reference circuit is open or high resistance
 
APP1 sensor VREF circuit is open or shorted to ground
 
APP sensor is damaged or it has failed
 
TAC module is damaged or it has failed
 

Trouble Code: P2125



Accelerator Pedal Position Sensor 2 Circuit Malfunction

Possible Causes:



APP1 sensor signal circuit is open or shorted to ground
 
APP1 sensor signal circuit is shorted to APP sensor 2 circuit
 
APP1 sensor signal circuit is open or shorted to VREF (5v)
 
APP sensor is damaged, or the TAC module is damaged or it has failed
 

Trouble Code: P2135



Throttle Position Sensor 1-2 Correlation Error

Possible Causes:



TP1 sensor signal circuit shorted to TP sensor signal 2 circuit
 
TP1 sensor signal circuit is shorted to the low reference circuit
 
TP2 sensor signal circuit is shorted to the low reference circuit
 
Throttle body assembly is damaged or it has failed
 

Trouble Code: P2146



Fuel Pump Relay Circuit Malfunction (Injectors 1, 4, 6 or 7)

Possible Causes:



Refer to repair information for P0201, P0204, P0206 or P0207
 
FICM (module) has failed (when P2146 is set all by itself)
 

Trouble Code: P2149



Fuel Pump Relay Circuit Malfunction (Injectors 2, 3, 5 or 8)

Possible Causes:



Refer to repair information for P0202, P0203, P0205 or P0208
 
FICM (module) has failed (when P2149 is set all by itself)
 

Trouble Code: P2665



AF Low Pressure Lock-Off Solenoid Circuit Malfunction

Possible Causes:



LPL solenoid control circuit is open or shorted to ground
 
LPL solenoid relay power circuit is open (test the AFS fuse)
 
LPL solenoid relay is damaged or it has failed
 
AF control module 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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