trouble code U0073

[lechez71]

i swapped a 5.3L from an 07 envoy in an 82 c10. got the harness reworked and ecm, tcm tuned. when i first got the harness and ecm back i connected and the motor turned on fine 2 days later just cranks does not start, i checked for codes and it read (U0073 con module comm bus off). any idea what it is?

[RedHeartbeat]

which vehicle and what year PCM?

[lechez71]

which vehicle and what year PCM?

the motor is from a 2007 gmc envoy denali, and so is the pcm. the harness, pcm, tcm, and motor, tranny all came out of the same vehicle.

[RedHeartbeat]

DTC U0073
Circuit Description

The GMLAN serial data circuits are controller area network (CAN) high speed serial data buses used to communicate information between the control modules. Typical data transmission speeds must be high enough to ensure that a required real-time response is maintained. Refer to Data Link Communications Description and Operation for the complete description of the buses used on this vehicle. The GMLAN serial data circuits also communicate directly to the data link connector (DLC). Messages are interpreted by the externally connected CANdi module which acts as a transceiver for the scan tool.
Modules connected to the GMLAN serial data circuits monitor communications during normal vehicle operation, where operation information is exchanged among the modules. All the modules on the GMLAN network, maintains a transmit error counter (TEC) and a receive error counter (REC). The counter values increase with detected errors and will decrease with error-free messages. If the TEC value exceeds 255, the controller removes itself from the network and DTC U0073 will result.
DTC Descriptor

This diagnostic procedure supports the following DTC:
DTC U0073 Controller Area Network (CAN) Bus Communication
Conditions for Running the DTCs
•
Supply voltage to the modules are in the normal operating range.


•
The vehicle is in the RUN power mode.

Conditions for Setting the DTC

The module setting the DTC has attempted to establish communications on the GMLAN circuits for more than 7 times.
Action Taken When the DTCs Sets
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The module suspends all message transmission.


•
The module inhibits the setting of all other communication DTCs.

Conditions for Clearing the DTC

•
A current DTC clears when the malfunction is no longer present.


•
A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Diagnostic Aids

•
This DTC cannot be retrieved with a current status. Diagnosis of a current DTC is accomplished via the symptom Scan Tool Does Not Communicate with High Speed GMLAN Device.


•
An intermittent condition is likely to be caused by a short on the GMLAN serial data circuits. Use the DMM MIN/MAX function to capture/locate intermittent conditions.

[RedHeartbeat]

Data Link Communications Description and Operation
Circuit Description

The serial data communication among the control modules is performed through multiple serial data communication links. The class 2 serial data line is always present. The high speed GMLAN or controller area network (CAN) may be present for different vehicle options. The data link connector (DLC) allows a scan tool to communicate with the modules on class 2 or high speed GMLAN serial data lines. In order for the scan tool to communicate with the modules on high speed GMLAN link, a CANdi module is needed. The CANdi module behaves as an interface between the scan tool and the high speed GMLAN data link. The CAN is used for functional communication only, among the modules connected to it.
Data Link Connector (DLC)

The data link connector (DLC) is a standardized 16 cavity connector. Connector design and location is dictated by an industry wide standard, and is required to provide the following:
•
Scan tool power battery positive voltage at terminal 16


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Scan tool power ground at terminal 4


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Common signal ground at terminal 5


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Class 2 signal at terminal 2


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High speed GMLAN serial data bus (+) at terminal 6


•
High speed GMLAN serial data bus (-) at terminal 14

Class 2 Serial Data Line

Class 2 serial data is transmitted on a single wire at an average of 10.4 kbps. This value is an average, class 2 uses a variable pulse width modulation to carry data and depending on the message it may operate faster or slower. The bus will float at a nominal 7 volts during normal operation. Each module can pull this lower during the transmission. The bus is not at battery positive voltage or ground potential during normal operation. When the ignition switch is in RUN, each module communicating on the class 2 serial data line sends a state of health (SOH) message every 2 seconds to ensure that the module is operating properly. When a module stops communicating on the class 2 serial data line, for example if the module loses power or ground, the SOH message it normally sends on the data line every 2 seconds disappears. Other modules on the class 2 serial data line, which expect to receive that SOH message, detect its absence; those modules in turn set an internal DTC associated with the loss of SOH of the non-communicating module. The DTC is unique to the module which is not communicating, for example, when the inflatable restraint sensing and diagnostic module (SDM) SOH message disappears, several modules set DTC U1088. Note that a loss of serial data DTC does not normally represent a failure of the module that set it.
The class 2 serial data line on this vehicle is a star configuration. The powertrain control module (PCM) has an additional class 2 serial data circuit to body control module (BCM). If one of the class 2 serial data circuits to the PCM opens, communication will not be interrupted. The following modules communicate on the class 2 serial data line:
•
The audio amplifier (AMP), w/UQ7 and Y91


•
The body control module (BCM)


•
The communication interface module (OnStar®), w/UE1


•
The digital radio receiver (DRR), w/U2K


•
The driver door module (DDM)


•
The electronic brake control module (EBCM)


•
The generator battery control module (GBCM)


•
The HVAC control module


•
The hybrid control module (HCM), w/HP2


•
The inflatable restraint sensing and diagnostic module (SDM)


•
The instrument panel cluster (IPC)


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The memory seat module (MSM), w/AN3


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The passenger door module (PDM)


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The powertrain/engine control module (PCM/ECM)


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The radio


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The rear seat audio (RSA) controller, w/UK6


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The rear seat entertainment (RSE) assembly w/U42


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The rear wheel steering control module (RWSCM), w/NYS


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The remote playback device - CD player (CDX), w/U1S


•
The transfer case shift control module (TCSCM), w/NP1/NP8


•
The transmission control module (TCM), w/M74

The class 2 serial data line allows a scan tool to communicate with these modules for testing purposes, checking for DTCs, and to activate/enable/disable functions. These class 2 serial data circuits are bussed together via 2 splice packs:

•
SP205--Located behind the instrument panel (I/P) near the headlamp switch connector.


•
SP207--Located in the I/P harness.

Refer to Computer/Integrating Systems Component Views .

Controller Area Network (CAN) Serial Data Line w/6.6L Engine

The controller area network (CAN) serial data line does not communicate with the scan tool via the data link connector (DLC). CAN serial data information is interpreted by the modules that are on the class 2 also, and transmitted to the scan tool. The following modules communicate on the CAN serial data line:
•
The engine control module (ECM)


•
The transmission control module (TCM)


•
The fuel injection control module (FICM)


•
The glow plug control module (GPCM)

The CAN serial data line, based on J1939 SAE standard, is high speed serial data bus used to communicate information among the modules. Typical data-transmission speeds must be high enough to ensure that the required real-time response is maintained.

The addressing scheme employed with CAN assigns a label to every message, with each message receiving a unique identifier. The identifier classifies the content of the message. Each module processes only those messages whose identifiers are stored in the module's acceptance list. This is CAN's form of message filtering.
The identifier labels both the data content and the priority of the message being sent. Each module can begin transmitting its most important data as soon as the bus is unoccupied. When more than one module starts to transmit simultaneously, the message with the highest priority is assigned first access. A module responds to failure to gain access by automatically switching to receive mode, the module then repeats the transmission attempt as soon as the bus is free again.
High Speed GMLAN Serial Data Line (PHT)

The data link connector (DLC) allows a scan tool to communicate with the high speed GMLAN serial data circuit through the CANdi module. The serial data is transmitted on two twisted wires that allow speed up to 500 Kbps. The twisted pair is terminated with two 120-ohm resistors, one is internal to the engine control module (ECM) and the other is internal to the energy storage control module (ESCM). The resistors are used to reduce noise on the high speed GMLAN bus during normal vehicle operation. The high speed GMLAN is a differential bus. The high speed GMLAN serial data bus (+) and high speed GMLAN serial data (-) are driven to opposite extremes from a rest or idle level. The idle level which is approximately 2.5 volts is considered a recessive transmitted data and is interpreted as a logic 1. Driving the lines to their extremes adds 1 volt to high speed GMLAN serial data bus (+) and subtracts 1 volt from high speed GMLAN serial data bus (-) wire. This dominant state is interpreted as a logic 0. GMLAN network management supports selective start up and is based on virtual networks. A virtual network is a collection of signals started in response to a vehicle event. The starting of a virtual network signifies that a particular aspect of the vehicles's functionality has been requested. A virtual network is supported by virtual devices which represents a collection of signals owned by a single physical device. So, any physical device can have one or more virtual devices. The signal supervision is the process of determining whether an expected signal is being received or not. Failsofting is the ability to substitute a signal with a default value or a default algorithm, in the absence of a valid signal. Some messages are also interpreted as a "heartbeat" of a virtual device. If such a signal is lost, the application will set a no communication code against the respective virtual device. This code is mapped as a code against the physical device. Note that a loss of serial data DTC does not normally represent a failure of the module that set it.
The powertrain control module (PCM) and hybrid control module (HCM) are functionally communicating on both class 2 and high speed GMLAN data links. However the diagnostic communication of the above modules with the scan tool is performed on class 2 data link only. All DTCs set by the high speed GMLAN modules, including HCM, are reported by the PCM on class 2. Data displaying, output controls and programming of the control modules connected to high speed GMLAN only, is performed through high speed GMLAN link.
The GMLAN serial data communications circuit is in a linear topology. The following modules are connected to the link, in order from DLC to the end of the linear configuration:
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The energy storage control module (ESCM)


•
The starter/generator control module (SGCM)


•
The electro-hydraulic power steering (EHPS)


•
The hybrid control module (HCM)


•
The powertrain control module (PCM)

[lechez71]

WOW thanks red, now i get an idea what it is.

[ducky]

dood greg did you have to link EVERYTHING lol

[RedHeartbeat]

damn bulletpoint format doesn't cut and paste well.