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Fig. 17 Power Brake Booster Hose
Fig. 18 Speed Control Vacuum
The engine controller has been programmed to monitor many different circuits of the fuel injection system. If a problem is sensed with a monitored circuit often enough to indicate an actual problem, the controller stores a fault. If the problem is repaired or ceases to exist, the engine controller cancels the Fault Code after 51 vehicle key on/off cycles.
Certain criteria must be met for a fault code to be entered into the engine controller memory. The criteria may be a specific range of engine RPM, engine temperature, and/or input voltage to the engine controller.
It is possible a fault code for a monitored circuit may not be entered into memory even though a malfunction has occurred. This may happen because one
of the fault code criteria for the circuit has not been met. For example, assume one of the fault code criteria for the MAP sensor circuit is the engine must be operating between 750 and 2000 RPM. If the MAP sensor output circuit shorts to ground when engine RPM is above 2400 RPM (resulting in a 0 volt input to the engine controller) a fault code will not be entered into memory. This is because the condition does not occur within the specified RPM range.
There are several operating conditions that the engine controller does not monitor and set fault codes for. Refer to Monitored Circuits and Non-Monitored Circuits in this section.
Stored fault codes can be displayed either by cycling the ignition key On - Off - On - Off - On, or through use of the Diagnostic Readout Box II (DRB II). The DRB II connects to the diagnostic connector in the vehicle (Fig. 15).
The engine controller can detect certain fault conditions in the fuel injection system.
Open or Shorted Circuit - The engine controller can determine if the sensor output (input to controller) is within proper range. Also, the controller can determine if the circuit is open or shorted.
Output Device Current Flow - The engine controller senses whether the output devices are hooked up. If there is a problem with the circuit, the controller senses whether the circuit is open, shorted to ground, or shorted high.
Oxygen Sensor - The engine controller can determine if the oxygen sensor is switching between rich and lean once the system has entered closed loop. Refer to Modes of Operation in this section for an explanation of closed loop operation.
NON-MONITORED CIRCUITS
The engine controller does not monitor the following circuits, systems and conditions that could have malfunctions that result in driveability problems. Fault codes may not be displayed for these conditions. However, problems with these systems may cause fault codes to be displayed for other systems. For example, a fuel pressure problem will not register a fault directly, but could cause a rich or lean condition. This could cause an oxygen sensor fault to be stored in the engine controller.
Fuel Pressure - Fuel pressure is controlled by the vacuum assisted fuel pressure regulator. The engine controller cannot detect a clogged fuel pump inlet filter, clogged in-line fuel filter, or a pinched fuel supply or return line. However, these could result in a rich or lean condition causing an oxygen sensor fault to be stored in the engine controller.
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Secondary Ignition Circuit - The engine controller cannot detect an inoperative ignition coil, fouled or worn spark plugs, ignition cross firing, or open spark plug cables.
Engine Timing - The engine controller cannot detect an incorrectly indexed timing chain, camshaft sprocket and crankshaft sprocket. However, these could result in a rich or lean condition causing an oxygen sensor fault to be stored in the engine controller.
Cylinder Compression - The engine controller cannot detect uneven, low, or high engine cylinder compression.
Exhaust System - The engine controller cannot detect a plugged, restricted or leaking exhaust system.
Fuel Injector Malfunctions - The engine controller cannot determine if a fuel injector is clogged, the needle is sticking or the wrong injector is installed. However, these could result in a rich or lean condition causing an oxygen sensor fault to be stored in the engine controller.
Excessive Oil Consumption - Although the engine controller monitors exhaust stream oxygen content when the system is in closed loop, it cannot determine excessive oil consumption.
Throttle Body Air Flow - The engine controller cannot detect a clogged or restricted air cleaner inlet or filter element.
Evaporative System - The engine controller will not detect a restricted, plugged or loaded evaporative purge canister.
Vacuum Assist - Leaks or restrictions in the vacuum circuits of vacuum assisted engine control system devices are not monitored by the engine controller. However, these could result in a MAP sensor fault being stored in the engine controller.
Engine Controller System Ground - The engine controller cannot determine a poor system ground. However, a fault code may be generated as a result of this condition.
Engine Controller Connector Engagement - The engine controller cannot determine spread or damaged connector pins. However, a fault code may be generated as a result of this condition.
The engine controller compares input signal voltages from each input device with established high and low limits for the device. If the input voltage is not within limits and other fault code criteria are met, a fault code will be stored in memory. Other fault code criteria might include engine RPM limits or input voltages from other sensors or switches that must be present before a fault condition can be verified.
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A fault code indicates that the engine controller has recognized an abnormal condition in the system. Fault codes can be obtained from the Check Engine lamp on the Instrument Panel or from the Diagnostic Readout Box II (DRBII). Fault codes indicate the results of a failure but do not identify the failed component directly.
WARNING: APPLY PARKING BRAKE AND/OR BLOCK WHEELS BEFORE PERFORMING ANY TEST ON AN OPERATING ENGINE.
(1)Connect DRBII to the diagnostic connector located in the engine compartment near the driver side strut tower (Fig. 15).
(2)Start the engine if possible, cycle the transmission selector and the A/C switch if applicable. Shut off the engine.
(3)Turn the ignition switch on, access Read Fault Screen. Record all the fault messages shown on the DRBII. Observe the check engine lamp on the instrument panel. The lamp should light for 2 seconds then go out (bulb check).
Fault code erasure; access erase fault code data
The switch inputs used by the engine controller have only two recognized states, HIGH and LOW. For this reason, the engine controller cannot recognize the difference between a selected switch position versus an open circuit, a short circuit, or a defective switch. If the change is displayed, it can be assumed that the entire switch circuit to the engine controller is functional. From the state display screen access either State Display Inputs and Outputs or State Display Sensors.
Connect the DRB II tester to the vehicle and access the State Display screen. Then access Inputs and Outputs. The following is a list of the engine control system functions accessible through the Inputs and Outputs screen.
Park/Neutral Switch
Speed Control Resume Brake Switch
Speed Control On/Off Speed Control Set A/C Switch Sense
Z2 Voltage Sense
S/C Vent Solenoid S/C Vacuum Solenoid
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A/C Clutch Relay
EGR Solenoid
Auto Shutdown Relay
Fuel Pump Relay
Radiator Fan Relay
Purge Solenoid
Check Engine Lamp
Connect the DRB II tester to the vehicle and access the State Display screen. Then access Sensor Display. The following is a list of the engine control system functions accessible through the Sensor Display screen.
Battery Temp Sensor
Oxygen Sensor Signal
Coolant Temp Sensor Throttle Position Minimum Throttle Battery Voltage MAP Sensor Reading AIS Motor Position Adaptive Fuel Factor Barometric Pressure Min Airflow Idl Spd Engine Speed
DIS Sensor Status Fault #1 Key-On Info Module Spark Advance Speed Control Target Fault #2 Key-on Info Fault #3 Key-on Info Speed Control Status
Speed Control Switch Voltage Overall Knock Retard Charging System Goal
Theft Alarm Status
Map Sensor Voltage Vehicle Speed Oxygen Sensor State MAP Gauge Reading Throttle Opening Total Spark Advance
The circuit actuation test mode checks for proper operation of output circuits or devices which the engine controller cannot internally recognize. The engine controller can attempt to activate these outputs and allow an observer to verify proper operation. Most of the tests provide an audible or visual indication of device operation (click of relay contacts, spray fuel, etc.). Except for intermittent conditions, if a device functions properly during testing, assume the device, its associated wiring, and driver circuit working correctly.
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Connect the DRB II tester to the vehicle and access the Actuators screen. The following is a list of the engine control system functions accessible through Actuators screens.
Stop All Tests
Ignition Coil #1
Ignition Coil #2
Ignition Coil #3
Fuel Injector #1
Fuel Injector #2
Fuel Injector #3
Fuel Injector #4
Fuel Injector #5
Fuel Injector #6
AIS Motor Open/Close Radiator Fan Relay A/C Clutch Relay Auto Shutdown Relay Purge Solenoid
S/C Serv Solenoids Alternator Field EGR Solenoid
All Solenoids/Relays
ASD Fuel System Test
(1)Warm engine in Park or Neutral until the cooling fan has cycled on and off at least once.
(2)Ensure that all accessories are off.
(3)Shut off engine.
(4)Disconnect the PCV valve hose from the intake manifold nipple.
(5)Attach Air Metering Fitting #6457 (0.125 in. orifice) to the intake manifold PCV nipple (Fig. 19).
Fig. 19 Air Metering Fitting #6457
(6)Disconnect the 3/16 inch idle purge line from the throttle body nipple. Cap the 3/16 inch nipple.
(7)Connect Diagnostic Readout Box II (DRB II).
(8)Restart the engine. Allow engine to idle for at least one minute.
(9)Using the DRBII, access Min. Airflow Idle Spd.
(10)The following will then occur:
²AIS motor will fully close.
²Idle spark advance will become fixed.