Powertrain Management: Description and Operation

The On-Board Diagnostic (OBD) System

The fuel and ignition systems are equipped with an OBD system with three diagnostic test modes (DTMs) to facilitate fault tracing.





The Data Link Connector (DLC) is located in the engine compartment by the left hand suspension tower. Output 2 is used for the fuel system and output 6 for the ignition system.

Faults are registered in DTM 1. If these faults are emission related a MIL is lit on the combination instrument. A maximum of three faults can be stored at one time (the fuel system OBD system for California models can store up to 17 DTCs).

Sensor signals are tested in DTM 2. DTM 2 can be activated manually by pressing the diagnostic button twice. The control module responds with a code if it receives a signal when the sensor is activated.

The signals to certain control components are tested in DTM 3. DTM 3 can be activated manually by pressing the diagnostic button three times. The control module then activates the control components one by one. Whether the component is operating is ascertained by listening or feeling it.

The Fuel System




The control module continually checks the following modes when the car is being driven:

- The control module's own internal functions

- HO2S and fuel trim

- ECT sensor

- MAF sensor

- Battery voltage

- TP switch

- Engine speed signal from the DI system control module

- Speedometer signal

- Knock enrichment signal from the DI system

- IAC valve

A fault in any of these functions is presented as a DTC in DTM 1

Checking For More Codes:

DTM 2 tests the signals from the following sensors:

-TP switch in full load position OK 3-3-3

-TP switch in idle position OK 3-3-2

-Engine speed signal from DI EZ 116K OK 3-3-1

-A/C control on/off OK 1-1-4

-A/C compressor start OK 1-3-4

-Engine speed compensation for automatic transmission OK 1-2-4

DTM 3 tests the signals to the following control components:

-Injectors

-IAC valve

-The carbon filter solenoid valve

-The cold start valve


The Distributor Ignition (DI) System

Entering Control Function #2:

The control module continually checks the following functions when the car is being driven:

- The control module's own, internal functions

- KS signal

- Fuel system load signal

- RPM sensor signal

- ECT sensor signal

- Signal from the vacuum controller

- Signal from the EGR temperature sensor

Entering Control Function #3:

A fault in any of these functions is presented as a DTC in DTM 1.

DTM 2 tests the signals from the following sensors:

-RPM sensor signal OK 1-4-1

-TP switch in idle position OK 3-3-4

DTM 3 tests signals to the EGR controller.