P1626
DTC P1626 VTD Controller Serial Data Circuit
Circuit Description
A Class II serial data communications system is used on this vehicle in order to allow various modules to communicate and share information with each other.
Each bit of information has one of two lengths: long or short. This allows for the reduction of the vehicle wiring, and for the transmission and reception of multiple signals over a single wire. The messages carried on the Class II serial data stream are also prioritized. If two messages attempt to establish communications on the data line at the same time, the message with the higher priority will continue. The message with the lower priority message will wait.
All modules on the Class II serial data line send out a periodic identifier message. The PCM is listening for the identifier messages from the EBCM and the Truck Body Controller (TBC) as well as an echo of the PCM identifier message. If a module cannot respond to the PCM, a DTC is stored.
Conditions for Setting the DTC
The PCM has lost communication with the Truck Body Controller (TBC) after the PCM received a Theft Passed message from the BFC.
Action Taken When the DTC Sets
- The PCM will record operating conditions at the time the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.
- A history DTC stores.
Conditions for Clearing the MIL/DTC
- A history DTC will clear after 40 consecutive warm up cycles without a fault.
- A scan tool can clear the DTC(s).
Diagnostic Aids
Attempting to start the vehicle by bypassing the Passlock II system or by substituting parts without performing the password learn procedure may set a DTC P1631 and a P1632.
If no password is received, a DTC U1064 and P1632 may be set.
An intermittent may be caused by a poor connection, a rubbed through wire insulation, or by a wire broken inside the insulation.
Thoroughly check any suspected circuitry for the following items:
- Backed out terminals or improper mating
- Broken locks
- Improperly formed or damaged terminals
- Poor terminal to wiring connections
- Physical damage to the wiring harness
- Corrosion
Test Description
The number(s) below refer(s) to the step number(s) on the Diagnostic Table.
1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the fault occurred. The scan tool stores this data for later reference.
2. A scan tool that cannot display the PCM data indicates that a short exists on the serial data circuit.
4. Because of the internal link of the serial data circuits within the PCM, it is necessary to disconnect the PCM electrical connector in order to determine which serial data circuit or the module that the short is in.
6. Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be preformed. Refer to the latest Isuzu Technical Communication System (ITCS) information for programming procedures and also refer to the CKP System Variation Learn Procedure for the crankshaft position variation learning procedure.
7. If the serial data circuit to the Truck Body Controller (TBC) was not open, this indicates that the serial communication loss to the PCM lies within the TBC. Refer to Truck Body Controller portion of the service manual for Passlock diagnosis.
8. If the serial data loss occurred after a good theft password has been received, the PCM will allow the vehicle to start on following attempts. After making the necessary repairs to the vehicle, reprogram the replacement PCM and complete the password learn procedure and the crankshaft position system variation learning procedures in order to allow the theft system to operate properly. Refer to the Password Learn Procedure portion of the service manual for the reprogramming procedures.
9. If no malfunctions are present at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.