Scan Tool Orientation
GENERAL DESCRIPTIONThe Engine Controller has been programmed to monitor many different circuits of the fuel injection system. If a problem is sensed in a monitored circuit often enough to indicate an actual problem, a fault is stored. It will be stored in the Engine Controller memory for eventual display to the service technician. If the problem is repaired or ceases to exist, the Engine Controller cancels the fault after 51 engine starts.
Certain criteria must be met for a fault to be entered into 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 that a fault for a monitored circuit may not be entered into memory even though a malfunction has occurred. This may happen because one of the fault criteria for the circuit has not been met. Example: assume that one of the criteria for MAP sensor circuit is that engine must be operating between 750 and 2000 rpm to be monitored for a fault. If the MAP sensor output circuit shorts to ground when engine rpm is above 2400 rpm, a 0 volt input will be seen by the Engine Controller. A fault will not be entered into memory 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 faults for. Refer to Monitored Circuits and Non-Monitored Circuits in this section.
Stored fault codes can be displayed by cycling the ignition key ON - OFF - ON - OFF - ON. They can also be displayed through use of a Diagnostic Scan Tool. The Scan Tool connects to the diagnostic connector in the vehicle.
MONITORED CIRCUITS
The engine controller can detect certain faults in its systems, the following is a list of the types of faults the engine controller can detect.
Open or Shorted Circuit - The engine controller can determine if the input signal from the sensor is within its range and if the sensor circuit is open or shorted.
Output Device Current Flow - The engine controller can see if the output devices are hooked up. If a problem exists with an output devices' circuit, the engine controller can determine if it is open, shorted high, or shorted to ground.
Oxygen Sensor - Once the system has entered closed loop, the engine controller checks that the oxygen sensor is switching between rich and lean. Refer to Powertrain Management/Computers and Control Systems/Electronic Control Module/Description and Operation.
NON-MONITORED CIRCUITS
The following circuits, systems and conditions that cause driveability problems are not monitored by the engine controller. Fault codes may not be displayed for these areas, but problems with them may cause fault codes to be displayed for other systems. For example, a fuel injector problem will not yield a fault directly, but could cause a rich or lean fuel mixture condition. This could cause an oxygen sensor fault to be stored in the engine controller.
Cylinder Compression - The engine controller cannot detect uneven, high, or low engine cylinder compression.
Engine Controller Connector Engagement - The engine controller cannot tell if connector pins are spread or damaged, but a fault code may be set as a result of this condition.
Engine Controller System Ground - The engine controller has no way of determining a poor system ground, but a fault may be generated if a poor system ground condition exists.
Engine Timing - The engine controller cannot tell if a cam gear, crank gear, or ignition distributor is indexed incorrectly. Any of the previous problems could result in a lean or rich air/fuel mixture, causing an oxygen sensor fault to be generated.
Evaporative System - The engine controller has no way to determine if the charcoal canister or its purge hoses are plugged, restricted, or loaded with fuel.
Excessive Oil Consumption - Even though the engine controller monitors exhaust oxygen content, via the oxygen sensor, when the vehicle is in closed loop, it cannot detect excessive oil consumption.
Exhaust System - The engine controller cannot determine or detect if an exhaust system is plugged, restricted, or leaking.
Fuel Pressure - Fuel pressure is controlled by the pressure regulator, and the pressure regulator is controlled by the vacuum signal sent from the throttle body. The engine controller cannot determine if the fuel pump pressure is too low or high, if the fuel filter is clogged, if the inlet or return lines are pinched or restricted, or if the fuel pump filter is clogged or restricted. Any of the previous problems could cause a lean or rich air/fuel mixture, resulting in an oxygen sensor code being generated.
Fuel Injector Malfunctions - The engine controller cannot determine if the wrong injector has been installed, if the pintle is clogged or stuck, or if the injector tip has completely worn out. Any of the previous problems could cause a lean or rich air/fuel mixture, resulting in an oxygen sensor code being generated.
Secondary Ignition Circuit - The engine controller cannot detect fouled or worn spark plugs, inoperative ignition coil, ignition cross firing, or open spark plug cables.
Throttle Body Air Flow - The engine controller cannot detect a clogged air filter element, a restricted air cleaner inlet, a dirty throttle body or plenum, or a clogged or dirty air bypass passage. Any of the previous problems could cause a lean or rich air/fuel mixture, resulting in an oxygen sensor code being generated.
Vacuum Assist - The engine controller cannot determine if the vacuum circuits of the vacuum assisted components have leaks, restrictions, or cracked hoses. Any of the previous problems could cause a MAP sensor fault to be generated.
HIGH AND LOW LIMITS
The Engine Controller compares input signal voltages from each input device. It will establish high and low limits that are programmed into it for that device. If the input voltage is not within specifications, and other fault criteria are met, a fault will be stored in memory. Other fault code criteria might include engine rpm limits or input voltages from other sensors or switches. The other inputs might have to be sensed by the controller when it senses a high or low input voltage from the control system device in question.
SCAN TOOL HOOK-UP
Connect the scan tool to the diagnostic connector located in the engine compartment. The separate red clip is connected to the positive post of the battery.
With the scan tool properly connected, all character positions on the display should briefly illuminate, and the copyright message should appear.
NOTE: At any time after the copyright screen, the user may press the F3 key for help.
A commonly reported problem is that the scan tool screen is blank. If the screen is blank after the scanner is attached to the vehicle, do the following:
- Make sure all cable connections are properly seated and fit snugly.
- Make sure the cables are in good condition (no broken or shorted wires).
- Make sure the cartridge is installed properly into the scan tool.
- Try the scan tool on another vehicle. If the scan tool screen is still blank, have the unit repaired. If it now performs properly, continue with next step.
Data Link Connector Identification:
- Make sure all cable connectors are in good condition (no flared or pushed out terminals). If the connector is good, continue with next step.
On-Board Diagnostic Connector Identification (Wire Color May Vary By Model):
- Check the BK/WT wire in the diagnostic connector for continuity to ground.
STATE DISPLAY TEST MODE
The switch inputs that are used by the engine controller have only two states, HI and LOW. Because of the logical process of the engine controller, it cannot determine the difference between a selected switch position and an open or shorted circuit, or a defective switch. If the change from OFF to ON or ON to OFF is displayed (scan tool) then it can be assumed that the entire switch circuit to engine controller is functional. Connect the scan tool to the vehicle and access "State Displays". Access "Inputs and Outputs" or "Sensors".
State Display Inputs and Outputs
- A/C Clutch Relay
- A/C Request Input
- A/C Select Switch
- Alternator Lamp
- Auto Shutdown Relay
- Ballast Bypass Relay
- Brake Switch
- Check Engine Lamp
- EMR Lamp
- Inverse J2 Voltage Sense
- Park/Neutral Switch
- Power Steering input (2.5L only)
- Radiator Fan Relay
- Speed Control Set
- Speed Control On/Off
- Speed Control Resume
- Speed Control Vent Solenoid
- Speed Control Vacuum Solenoid
- Starter Switch Sense
- Up-shift Indicator Lamp
- Z2 Voltage Sense
State Display Sensors
- Adaptive Fuel Factor
- Added Adaptive Fuel Factor
- AIS Motor Position
- Barometric Pressure
- Battery Temperature
- Battery Voltage
- Charge Temperature (Air/Fuel)
- Charge (MAT) Temperature Sensor
- Charging System Goal
- Coolant Temperature
- Coolant Temperature Sensor
- Engine Speed
- Fault #1 Key-On Info
- Fault #2 Key-On Info
- Fault #3 Key-On Info
- MAP Gauge Reading
- MAP Sensor Reading
- MAP Sensor Voltage
- Minimum Throttle
- Minimum Air Flow Idle Speed
- Module Spark Advance
- Oxygen Sensor Signal
- Oxygen Sensor State
- Throttle Opening
- Throttle Position
- Total Spark Advance
- Vehicle Speed
CIRCUIT ACTUATION TEST MODE
The circuit actuation test mode checks for the proper operation of output circuits and devices that the engine controller cannot test. The engine controller attempts to actuate these outputs and allows an observer to verify the operation of the component. Most of the checks in this mode provide an audible or visual indication of component operation. Unless an intermittent condition exists, if a device functions properly during its test, it can be assumed that the component and its related circuit are functioning properly. To enter circuit actuation mode, access the "Actuators" screen on the scan tool.
The following can be tested in this mode:
- Air conditioning clutch relay
- All solenoids/relays
- Alternator field
- Automatic Idle Speed (AIS) motor open/close
- Auto shutdown (ASD) relay
- ASD fuel system test
- Fuel injector #1
- Fuel injector #2
- Fuel injector #3
- Fuel injector #4
- Fuel Injector #5 (if equipped)
- Fuel Injector #6 (if equipped)
- Fuel Injector #7 (if equipped)
- Fuel Injector #8 (if equipped)
- Ignition coil
- Stop All Tests
- Tachometer Output
- Up-shift indicator lamp