The Chrysler fuel injection systems combine electronic spark advance and fuel control. At the center of these systems is a digital, pre-programmed computer, known as a Single Module Engine Controller (SMEC) for 1987-89, a Single Board Engine Controller (SBEC) for 1990-91, a Single Board Engine Controller II (SBEC II) for 1992 and a Powertrain Control Module (PCM) for 1993-95. The SMEC, SBEC, SBEC II or PCM regulates ignition timing, air-fuel ratio, emission control devices, cooling fan, charging system idle speed and speed control. It has the ability to update and revise its commands to meet changing operating conditions.
Various sensors provide the input necessary for controller to correctly regulate fuel flow at the injectors. These include the Manifold Absolute Pressure (MAP), Throttle Position Sensor (TPS), oxygen sensor, coolant temperature sensor, charge temperature sensor, and vehicle speed sensors.
In addition to the sensors, various switches are used to provide important information to the controller. These include the neutral safety switch, air conditioning clutch switch, brake switch and speed control switch. These signals cause the SMEC, SBEC, SBEC II or PCM to change either the fuel flow at the injectors or the ignition timing or both.
The SMEC, SBEC, SBEC II or PCM , are designed to test their own input and output circuits, If a fault is found in a major system, this information is stored in the SMEC, SBEC, SBEC II or PCM for eventual display to the technician. Information on this fault can be displayed to the technician by means of the instrument panel CHECK ENGINE light or by connecting a diagnostic read-out tester and reading a numbered display code, which directly relates to a general fault. Some inputs and outputs are checked continuously and others are checked under certain conditions. If the problem is repaired or no longer exists, the The SMEC, SBEC, SBEC II or PCM cancels the fault code after 50-100 key ON/OFF cycles.
When a fault code is detected, it appears as either a flash of the CHECK ENGINE light on the instrument panel or by watching the Diagnostic Readout Box II (DRB II). This indicates that an abnormal signal in the system has been recognized by the SMEC, SBEC, SBEC II or PCM . Fault codes do indicate the presence of a failure but they don't identify the failed component directly.
Fault codes are 2 digit numbers that tell the technician which circuit is bad. Fault codes do indicate the presence of a failure but they don't identify the failed component directly. Therefore a fault code and a result are not always the reason for the problem.
Indicator codes are 2 digit numbers that tell the technician if particular sequences or conditions have occurred. Such a condition where the indicator code will be displayed is at the beginning or the end of a diagnostic test. Indicator codes will not generate a CHECK ENGINE light or engine running test code.
ACTUATOR TEST MODE (ATM) CODES
ATM test codes are 2 digit numbers that identify the various circuits used by the technician during the diagnosis procedure.
ENGINE RUNNING TEST CODES
Engine running test codes are 2 digit numbers. The codes are used to access sensor readouts while the engine is running and place the engine in particular operating conditions for diagnosis.
CHECK ENGINE LIGHT
The CHECK ENGINE light has 2 modes of operation: diagnostic mode and switch test mode.
If a DRB II diagnostic tester is not available, the PCM/SMEC/SBEC can show the technician fault codes by flashing the CHECK ENGINE light on the instrument panel in the diagnostic mode. In the switch test mode, after all codes are displayed, switch function can be confirmed. The light will turn on and off when a switch is turned ON and OFF .
Even though the light can be used as a diagnostic tool, it cannot do the following:
- Once the light starts to display fault codes, it cannot be stopped. If the technician loses count, he must start the test procedure again.
- The light cannot display all of the codes or any blank displays.
- The light cannot tell the technician if the oxygen feed-back system is lean or rich and if the idle motor and detonation systems are operational.
- The light cannot perform the actuation test mode, sensor test mode or engine running test mode.
Be advised that the CHECK ENGINE light can only perform a limited amount of functions and is not to be used as a substitute for a diagnostic tester. All diagnostic procedures described herein are intended for use with a Diagnostic Readout Box II (DRB II) or equivalent tool.
The following diagnostic and test procedures are intended for use with the Diagnostic Readout Box II (DRB II). Since each available diagnostic readout box may differ in its interpretation and display of the sensor results, refer to the instructional procedure that accompanies each tester unit.Obtaining Fault Codes
- Connect the readout box to the diagnostic connector located in the engine compartment near PCM/SMEC/SBEC.
- Start the engine, if possible, cycle the transaxle selector and the A/C switch, if applicable. Shut off the engine.
- On 1988 models, turn the ignition switch ON, OFF, ON, OFF, ON within 5 seconds. On 1989-95 models, simply turn the ignition switch ON to access the read fault code data. Record all the fault code messages displayed on the readout box.
- Observe the CHECK ENGINE light on the instrument panel. The light should illuminate for 3 seconds and then go out.
EXITING THE DIAGNOSTIC TEST
By turning the ignition switch to the OFF position, the test mode system is exited. With a Diagnostic Readout Box attached to the system and the ATM control button not pressed, the computer will continue to cycle the selected circuits for 5 minutes and then automatically shut the system down.