Manual Transmission, Light Duty

OBD Diagnostic System Check:

Diagnostic Circuit:

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Checks for proper operation of the "Service Engine Soon" light. With the key "ON," and the engine not running, the light should be "ON" steady.

2. Grounding the diagnostic terminal will flash a Code 12 and any stored codes. The light must go "ON" and "OFF," for a proper code. If the light goes from "bright" to "dim," this is not considered a code.


CIRCUIT DESCRIPTION
The control module provides the diagnostic logic to detect faults in the systems that the control module monitors or controls. The control module, when it recognizes a fault, has the capability of turning a "Service Engine Soon" (SES) light "ON" and storing a code. Furthermore, if the condition corrects itself, the "Service Engine Soon" signal will be turned "OFF immediately following the correction

The control module recognizes errors in engine speed, vehicle speed vacuum errors in the EGR vacuum loop, via the MAP sensor, and electrical faults involving the 5 volt reference circuit.

The control module is a multifunction controller that controls the following:

^ Exhaust Gas Recirculation (EGR).
^ Exhaust Pressure Regulation (EPR).
^ System Diagnosis.
^ Cold Advance and Glow Plug.

The control module monitors the following inputs, to allow proper control of the above.

^ Engine rpm.
^ Manifold Absolute Pressure (MAP) used to monitor EGR vacuum.
^ Throttle Position Sensor (TPS).
^ Vehicle Speed Sensor (VSS).
^ Engine Coolant Temperature Sensor (ECT).

All diagnosis should start with the "Diagnostic Circuit Check/OBD".

After any repair to the diesel electronic control system, the "Diagnostic Circuit Check/OBD" must be repeated.

A brief description of operation is included with each system check or code chart.