Diagnostic Trouble Codes (DTCs)
Network Codes

Diagnostic Trouble Codes for OBD II (OBD2) equipped General Motors (GMC, Chevrolet, Buick, Oldsmobile, Cadillac, Pontiac, Saturn) vehicles.

Updated through the 2004 model year.

All cars and light trucks built and sold in the United States after January 1, 1996 were required to be OBD II equipped. In general, this means all 1996 model year cars and light trucks are compliant, even if built in late 1995. Some 1995 model year vehicles are also equipped with OBDII - although some pre-1996 OBD-II cars are not 100% compliant. Pre-OBD-II cars had connectors in various positions under the dashboard and under the hood. All OBD-II cars have a connector located in the passenger compartment easily accessible from the driver's seat.

GM cars and light trucks use SAE J1850 VPW (Variable Pulse Width Modulation). There are some variations among imports such as the Cadillac Catera, which is a German Opel derivative, the Catera uses the European ISO 9141 protocol.

A cable is plugged into the OBD-II J1962 connector and the other end is connected to a scan tool. A hand-held scan tool is usually limited to one OBD-II system type - there are three basic OBD-II protocols in use, each with minor variations on the communication pattern between the on-board diagnostic computer and the scan tool. In general, Chrysler products and all European and most Asian imports use ISO 9141 circuitry. GM cars and light trucks use SAE J1850 VPW (Variable Pulse Width Modulation), and Fords use SAE J1850 PWM (Pulse Width Modulation) for communication.

A complete driving cycle will perform diagnostics on all monitored systems and can usually be completed in less than fifteen minutes.

Performing a GM OBDII Driving cycle:

1. Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 122°F (50°C) and within 11°F (6°C) of the ambient air temperature at startup. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.
2. Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.
3. Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 55mph (88km/hr) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.
4. Hold Steady Speed. Hold a steady speed of 55mph (88km/hr) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.
5. Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 20 mph (32km/hr). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.
6. Accelerate. Accelerate at 3/4 throttle until 55-60mph (88-96 km/hr). This will perform the same diagnostics as in step 3.
7. Hold Steady Speed. Hold a steady speed of 55mph (88km/hr) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.
8. Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.

How the Diagnostic Trouble Code is created: A DTC is made up of 5 digits. The chart below shows the composition of a DTC. With this information you can easily determine what system to trouble shoot without knowing the exact description of the code.

                 X  X  X  X X
                 |  |  |   |
                 |  |  |   |
B Body ----------+  |  |   +-- Fault (00 to 99)
C Chassis -------+  |  |
P Powertrain ----+  |  |
U Network -------+  |  +------ 1 Fuel & Air Metering
                    |  +------ 2 Fuel & Air Metering (Injector)
                    |  +------ 3 Ignition System or Misfire
0 SAE --------------+  +------ 4 Auxiliary Emission Controls
1 MFG --------------+  +------ 5 Vehicle Speed & Idle Control System
                       +------ 6 Computer Output Citcuit
                       +------ 7 Transmission
                       +------ 8 Transmission
                       +------ 9 Reserved
                       +------ 0 Reserved

Using the Cadillac on-board diagnostic display you'll also see "IP" for the IPC instrument panel, "AC" for the air conditioning module, "TC" for traction control, "RS" for the road suspension system, "SD" for the air bags, "PZ" for the body control module, "CC" for the cell phone and "RF" for the integrated radio.

There are two categories of DTC's that apply to OBDII.

Type A

1. Emissions related.
2. Requests illumination of the MIL after one failed driving cycle.
3. Stores a freeze frame DTC after one failed driving cycle.
Type B

1. Emissions related.
2. Sets a Pending Trouble Code after one failed driving cycle.
3. Clears a Pending Trouble Code after one successful driving cycle.
4. Turns on the MIL after two consecutive failed driving cycles.
5. Stores a freeze frame after two consecutive failed driving cycles.

• Manufacture Codes -- DTC 01 - 199
• "B" Body Codes -- B0001 - B4000
• "C" Chassis Codes -- C0000 - C1800
• "P" Powertrain Codes -- P0016 - P2800
• "U" Network Codes -- U0001 - U2200

• U0001 - Controller Area Network (CAN) Bus Communication (ECM)
• U1000 - Class 2 Communication Malfunction
• U1001~U1254 - Loss of XXX Communications
• U1002~U1015 - Loss of serial communications for class 2 devices
• U1016 - Loss of Class 2 Communication with VCM
• U1016 - Loss of Communications with PCM
• U1017~U1025 - Loss of serial communications for class 2 devices
• U1026 - Loss of ATC Class 2 Communication
• U1027~U1039 - Loss of Serial Communications for Class 2 Devices
• U1040 - Loss of Class 2 Communications with ABS
• U1041 - Loss of EBCM Communication
• U1042 - Lost Communications with Brake/Traction Control System
• U1043~U1055 - Loss of Serial Communications for Class 2 Devices
• U1056 - Loss of Communications with RSS
• U1057~U1060 - Loss of Serial Communications for Class 2 Devices
• U1161 - Loss of PDM Serial Data
• U1062 - Loss of Serial Communications for Class 2 Devices
• U1163 - Loss of RRDM Serial Data
• U1064 - Loss of Communications with DIM
• U1065 - Loss of Communications with IPM
• U1066 - Loss of Communications with RIM
• U1067~U1069 - Loss of Serial Communications for Class 2 Devices
• U1170 - Loss of Driver Door Switch Asm Serial Data
• U1071~U1087 - Loss of Serial Communications for Class 2 Devices
• U1088 - Loss of Communications with SDM
• U1089~U1095 - Loss of Serial Communications for Class 2 Devices
• U1096 - Loss of Communications with IPC
• U1097~U1127 - Loss of serial communications for class 2 devices
• U1128 - Loss of Communications with IRC
• U1129 - Loss of Communications with AMP
• U1130~U1143 - Loss of serial communications for class 2 devices
• U1144 - Loss of Communications with PHN
• U1145 - Loss Of NAV Communications
• U1146 - Loss Of Onstar Communiction
• U1147~U1151 - Loss of serial communications for class 2 devices
• U1152 - Loss Of ACM Serial Data Communication
• U1152 - Loss of Data HCM
• U1153 - Loss of Communications with CCP
• U1154~U1159 - Loss of serial communications for class 2 devices
• U1160 - Loss of Communications with DDM
• U1161 - Loss of PASS Door Module SBI
• U1162 - Loss of Rear Driver Door Module SBI
• U1163 - Loss of Rear PASS Door Module SBI
• U1164 - Loss Of DIM Serial Data Communication
• U1165 - Loss of serial communications for class 2 devices
• U1166 - Loss of Communications with SCM
• U1167 - Loss of serial communications for class 2 devices
• U1168 - Loss Of TTM Communications
• U1169 - Loss of Communications with MMM
• U1170 - Loss of Driver Door Switch SBI
• U1171~U1175 - Loss of serial communications for class 2 devices
• U1176 - Loss Of RFA Communications
• U1177~U1191 - Loss of serial communications for class 2 devices
• U1192 - Loss of VTD Class 2 Serial Data Com
• U1193 - Loss of VIM Class 2 Communication
• U1194~U1254 - Loss of serial communications for class 2 devices
• U1255 - Class 2 Communication Malfunction (Serial Data Line Malfunction)
• U1300 - Class 2 Short to Ground
• U1301 - Class 2 Short to Battery
• U1304 - Loss Of UART Communications
• U1305 - Class 2 Data Link Low or High
• U1500 - Inter-Device Dedicated Bus Malfunction
• U1713 - Loss of Front Door Module to Window Motor High Speed Comm.
• U1715 - Loss of Front Door Module to Window Motor High Speed Comm.
• U1714 - Loss of Front Door Module to Window Motor Normal Speed Comm.
• U1716 - Loss of Front Door Module to Window Motor Normal Speed Comm.
• U1800 - Controller Area Network (CAN) Bus Communication
• U2000 - Invalid BFC Transmitted SPI Data
• U2001 - Invalid IPC Transmitted SPI Data
• U2002 - SPI Data-In Low
• U2003 - SPI Data-In High
• U2004 - SPI Data-Out Low
• U2005 - SPI Data-Out High
• U2006 - SPI Clock-Out Low
• U2007 - SPI Clock-Out High
• U2050 - SIR PPS/CPS Communications Link malfunction
• U2100 - Controller Area Network (CAN) Bus OFF
• U2100 - CAN-BUS Communication Malfunction
• U2102 - More Controllers on Bus than Programmed
• U2103 - Fewer Controllers On Bus Than Programmed
• U2104 - CAN Bus Reset Counter Overrun
• U2105 - CAN Bus Error ECM
• U2105 - Lost Comm with Engine Control System
• U2106 - Lost Comm with Trans Control System
• U2107 - Lost Communications with Body Control System
• U2108 - CAN Bus Error ABS
• U2108 - Lost Comm with ABS Control System
• U2150 - Navigation ECU Gateway Communication Error
• U2151 - Navigation ECU Communication Malfunction
• U2153 - VICS ECU Communication Error

This information applies to all GM vehicles Using Class 2 communication.

DTC U1000 or U1255 may set current or history, with or without other DTCs.

These DTCs set when the control module does not receive a message that it was expecting from another control module, and does not know which control module did not send the message.

1. If the DTC U1000 or U1255 is set in history with other DTCs set current or history, diagnose the other DTCs first.
2. If the DTC U1000 or U1255 is set current, this usually indicates a module that is currently not communicating or a configuration issue. For example, if the control module is configured for an option (i.e., OnStar, keyless entry, memory mirrors, etc.) that the vehicle does not have, it may expect to receive a message regarding this missing feature. This would usually occur due to the control module being recently replaced and incorrectly set up.
3. When the DTC U1000 or U1255 is current, the module that is not communicating may not even be listed on the Tech 2 on the Diagnostic Circuit Check /Class 2 Message Monitor list.
4. If the DTC U1000 or U1255 has set in history without other DTCs, replacing the control module that set the DTC is most likely NOT the solution. The module that has set the code is looking for an input from another module that is not communicating. Because the module did not receive an input that it is expecting to see, it sets a U1000 or U1255 which indicates there was a loss of communications. Look at the customer's concern (i.e., intermittent, erratic tachometer operation). This will probably be a better indication of the control module that is the source of the concern.

• Manufacture Codes -- DTC 01 - 199
• "B" Body Codes -- B0001 - B4000
• "C" Chassis Codes -- C0000 - C1800
• "P" Powertrain Codes -- P0016 - P2800
• "U" Network Codes -- U0001 - U2200

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