For 1990-2009 cars

Refer to

#### Cell 21: Fuel Controls

Engine Controls Component Views
Information Sensors/Switches Description
Cell 21: Fuel Injectors
Cell 21: Ignition Controls
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Ground Distribution Schematics
Ground Distribution Schematics

### Circuit Description

A Class Il serial data communications system is used on this vehicle 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 vehicle wiring to be reduced and the transmission and reception of multiple signals over a single wire. The messages carried on a Class II serial data streams 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. If a module cannot respond to the PCM, a DTC is stored.

### Conditions for Running the DTC

The VTD system has allowed fuel delivery.

### Conditions for Setting the DTC

The PCM has detected a loss of the state of health serial data message from the VTD system.

### Action Taken When the DTC Sets

• | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.

• | A history DTC is stored.

### Conditions for Clearing the MIL/DTC

• | A history DTC will clear after 40 consecutive warm up cycles without a fault.

• | DTCs can be cleared by using a scan tool.

### Diagnostic Aids

For complete serial data line schematics and VTD system diagnosis, refer to Electrical Diagnosis.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for the following conditions:

Important: Several BFC diagnostic procedures call for disconnecting the BFC and then turning the vehicle ignition to the RUN position. These procedures will result in the PCM setting DTC P1626. Therefore, DTC P1626 stored in history may be the result of previous BFC diagnostic work.

• | Intermittent short circuit on the serial data circuit. Refer to Scan Tool Does Not Communicate with Components in Data Link Communications. Be sure to check all related wiring for an intermittent short to ground or short to voltage.

• | Poor connection. Inspect the PCM and BFC harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

• | Damaged harness. Inspect the wiring harness for damage. Check for an intermittent short or open circuit in the wiring harnesses related to the BFC, including the ignition, battery feed, ground, and serial data circuits.

Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals and Connector Repairs in Wiring Systems.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

### Test Description

The numbers below refer to the step numbers on the diagnostic table:

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. A scan tool that cannot display PCM data indicates that a short exists on the serial data circuit.

3. The replacement PCM must be reprogrammed and the crankshaft position system variation procedure must be performed.

   If the serial data loss occurred after a good theft password has been received, the PCM must be reprogrammed and the password learn and the crankshaft position variation learn procedures must be completed to allow the theft system to operate properly.

4. If the serial data circuit to the Body Function Controller (BFC) was not open, then the serial communication loss to the PCM lies within the BFC. Refer to Body Function Controller portion of the service manual for Passlock diagnosis.

5. If no malfunctions have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.

#### DTC P1626 - No Password Received from Body Function Controller (BFC)

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain on Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Install a scan tool. Was DTC P1610 also set? | -- | GO to DTC P1610 Lost Communications with Body Multiple Control (BCM) System | Go to Step 3
3 | Has any part of the vehicle theft deterrent system been tampered with? | -- | Go to Step 4 | Go to Step 5
4 | Repair tampered component. Perform the Passlock learn procedure. Refer to Password Learn Procedure . Is the action complete? | -- | Go to Step 8 | --
5 | Momentarily rotate the ignition cylinder to crank without starting the vehicle. Does the BFC indicate the password is valid? | -- | Go to Step 6 | Go to Step 7
6 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | Go to Step 8 | --
7 | Check for BFC DTCs and make any necessary repairs. Is the action complete? | -- | Go to Step 8 |
8 |

1. Using the scan tool, clear DTCs.
2. Start engine and idle at normal operating temperature.
3. Operate vehicle within the conditions for setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic ran and passed?

--

Go to Step 9

Go to Step 2

9 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC | System OK