Engine Controls System Diagnosis
FROM SERVICE MANUAL, SECTION 6: ENGINE CONTROLS
Circuit Description
The class 2 circuit connects to various modules. These modules monitor the link for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules on the data link. When a module receives a critical operating parameter from another module, the receiving module records the identification number from the module that sent the message. This is called State of Health Monitoring (SOH). A critical operating command will have the sending module's identification number attached with it. Once an identification number is learned by a module, it will continue to monitor for that number. When no message is detected from a learned identification number for a set time, a code is set in the module that was monitoring the identification number.
Conditions for Running the DTC
The ignition voltage is greater than 9.5 volts, but less than 18.0 volts.
Conditions for Setting the DTC
^ The PCM does not detect a valid Class 2 message.
^ The PCM detects a high voltage (Class 2 circuit shorted to a voltage) on the Class 2 circuit.
^ All conditions met for 3.0 seconds.
Action Taken When the DTC Sets
^ The PCM stores the DTC information into memory when the diagnostic runs and fails.
^ The Malfunction Indicator Lamp (MIL) will not illuminate.
^ The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.
Conditions for Clearing the MIL/DTC
^ A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
^ A last test failed (Current DTC) will clear when the diagnostic runs and does not fail.
^ Use a scan tool in order to clear the MIL/DTC.
Diagnostic Aids
This DTC cannot be displayed on a scan tool when the fault is active. The scan tool will not communicate with an active DTC U1301.
The communication DTCs are for information only.
FROM SERVICE MANUAL, SECTION 8: WIRING SYSTEMS
CIRCUIT DESCRIPTION
Modules connected to the class 2 serial data link monitor the link for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. In addition to this, Node Alive (State of Health) messages are transmitted by each module on the class 2 serial data link about once every 2 seconds. When the module detects no messages and a high voltage on the class 2 serial data link for approximately 3 seconds, U1301 is set and the setting of all other class 2 serial communication DTCs is inhibited.
CONDITIONS FOR SETTING THE DTC
^ Voltage supplied to the module is in the normal operating voltage range (approximately 9-16 volts).
^ No valid class 2 messages are detected on the class 2 serial data link is high.
^ The voltage level detected on the class 2 serial data link is high
^ The above conditions are all met simultaneously for three seconds.
ACTION TAKEN WHEN THE DTC SETS
^ The module inhibits the setting of all other class 2 DTCs.
^ DTC U1301 is set by the module.
CONDITIONS FOR CLEARING THE DTC
^ A current U1301 will clear when a valid class 2 message is detected on the class 2 serial data link or at the end of the current ignition cycle.
^ A history U1301 will clear upon receipt of a scan tool Clear DTCs command.
DIAGNOSTIC AIDS
This DTC cannot be retrieved with a current status. Diagnosis of a current U1301 is accomplished via the symptom. The scan tool will not communicate with a class 2 device. An intermittent condition is likely to be caused by a short to voltage on the class 2 serial data link.