Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC U1818 00: Lost Communication With ECM/PCM A on Bus BDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
ECM B+ | 1* | 1* | -- | -- |
ECM Ground | -- | 1* | -- | -- |
PTLAN + | U0074* | U1818*, U189A | U0074* | -- |
PTLAN - | U0074* | U1818*, U189A | U0074* | -- |
* Other modules/DTCs will set with this fault. 1. Multiple DTCs including U1818 may set, and multiple symptoms including no start may occur | ||||
Circuit/System Description
Modules connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.
DTC U1818 will set in the serial data gateway module (SDGM) when no communication is established with the ECM on the PTLAN serial data bus.
Conditions for Running the DTC
| • | The system voltage is between 9-16 volts. |
| • | The vehicle power mode master requires serial data communication to occur from this specific module. |
Conditions for Setting the DTC
A supervised periodic message that includes the transmitter module availability has not been received.
Action Taken When the DTC Sets
The modules is never signaled, therefore the specific subsystems will not function.
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 of 50, without a repeat of the malfunction. |
Diagnostic Aids
| • | When testing circuits to the SDGM access can be accomplished by removing the instrument panel center trim panel. Note that this procedure does not allow removal of the SDGM, only access to the connector. Refer to Instrument Panel Center Trim Panel Replacement . |
| • | If the ECM is inoperative due to an open in the voltage or ground circuits then DTC U0100 will be set current in the power steering control module (PSCM). |
| • | Different DTCs may set in different modules along with this DTC depending on where the fault occurs and the vehicle operating conditions when the fault occurs. |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Circuit/System Verification
Verify the following DTCs are not set in the modules as follows:
| • | PSCM - U0100 |
| • | SDGM - U189A |
| ⇒ | If any listed DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle to diagnose that DTC prior to this diagnostic. |
Circuit/System Testing
- Ignition OFF, disconnect harness connector X1 of the APM and the EBCM.
- Test for less than 1.0 ohm between the APM and the EBCM on the following circuit terminals.
- Ignition OFF, disconnect harness connector X1 of the SDGM.
- Test for less than 1.0 ohm between the EBCM and the SDGM on the following circuit terminals.
- If the circuits test normal, replace the SDGM.
| • | PTLAN + APM terminal 5 and EBCM terminal 33 |
| • | PTLAN - APM terminal 1 and EBCM terminal 21 |
| ⇒ | If greater than the specified range, test the circuit for an open/high resistance. |
| • | PTLAN + EBCM terminal 34 and SDGM terminal 13 |
| • | PTLAN - EBCM terminal 22 and SDGM terminal 11 |
| ⇒ | If greater than the specified range, test the circuit for an open/high resistance. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for module replacement, setup, and programming |
