Scan Tool Testing and Procedures

The MPI engine management system has a self diagnostic mode where it actually operates specific output devices in sequence. This allows technicians to check (audibly or with DVM) whether or not certain devices and circuits are working. This "output check" mode is initiated in similar manner as the fault memory display, except that you start with the ignition turned "off". Vehicles produced before March 1990 have eight separate output checks generated in a specific order, each with its own identifying code and separated by an activation step which the technician must manually perform. Once the first output check is initiated, each time the jumper wire is connected between test connectors for 4 seconds, the next output check is initiated. In this way, if you only wanted to test the idle stabilizer valve (7th output check), you can simply step through the other checks.

NOTE: The "output checks" test the electrical circuits, solenoids, and output signals from the ECU. These checks do not necessarily test the mechanical portions of electro/mechanical devices such as fuel injectors or other solenoid type valves. Additional tests may be necessary, to verify the operating condition of these devices.

Output checks will occur in the following order:

1. Code 4433 - Fuel pump relay check (tests the ability of the fuel pump relay to turn the pump "on" by deliberately creating an output signal to energize the relay so the technician can monitor the fuel pump to find out if it is turning "on").

2. Code 4411 - Fuel injector, cylinder #1 (checks operation of fuel injector by turning it on and off 5 times).

3. Code 4412 - Fuel injector, cylinder #2 (turns on and off 5 times).

4. Code 4413 - Fuel injector, cylinder #3 (turns on and off 5 times).

5. Code 4414 - Fuel injector, cylinder #4 (turns on and off 5 times).

6. Code 4421 - Fuel injector, cylinder #5 (turns on and off 5 times).

7. Code 4431 - Idle stabilizer valve (valve turns on and off while code is displayed. Listen for clicking).

8. Code 4343 - Carbon canister frequency valve check (solenoid clicks on and off, tests solenoid and wiring by deliberately creating an output signal to the solenoid so the technician can monitor it for a response).

9. Code 0000 - End of output checks.


ACTIVATING OUTPUT CHECKS
After having displayed and recorded all fault codes, use the following procedure to perform output checks.

Diagnostic Connectors - Activating Self Diagnostics:

1. With ignition turned "off", connect LED test light and jumper wire to terminals of diagnostic connectors, as when performing fault memory display. Make sure jumper wire is connected to both connectors, and leave connected until after ignition is turned on.

2. Turn ignition "on" but do not start engine. Check engine light (or LED) should light up. Wait at least 4 seconds then disconnect jumper wire from brown connector. The first output check is now activated. A code 4433 should be displayed. In this mode, the codes are output codes and indicate which device or circuit is being tested.

^ Fuel pump should run while code 4433 is being displayed (listen for "humming" sound from pump, should be audible). If fuel pump does not run, check pump, fuse, wiring and relay individually, after output checks are complete.

3. Switch to the next step by reconnecting jumper wire for 4 seconds, then remove. The next output check is now activated. Code 4411 should display.

4. Open the throttle all the way to the full throttle stop, then release.

^ Fuel injector for cylinder #1 should click on and off 5 times. Listen for clicking.

NOTE: These injectors are very quiet. If no clicking can be heard, you may want to connect another LED test light in place of the injector, and watch for the light to flash instead, or use a stethoscope type listening device.

5. The next output check code is activated each time you reconnect the jumper wire. Repeat steps 3 and 4 to check each of the remaining four injectors.

6. After all of the injectors have been checked, reconnect the jumper wire for 4 seconds to activate the next output check. Code 4431 should display. Listen for the idle stabilizer valve to click on and off.

NOTE: It is not necessary to open the throttle valve to initiate the output checks for the idle stabilizer valve or carbon canister frequency valve.


7. Activate the next output check (reconnect the jumper wire for 4 seconds to activate the next output check). Code 4343 should display. Listen for the carbon canister frequency valve to click on and off.

If any device for which there is an output check has failed its test, check wiring and connections, and repair as necessary.

If ECU will not enter output check mode, check continuity of wires between diagnostic connectors and control unit. Also check for power at top terminal of diagnostic connector #1 (should have battery power), and check ECU and wire at bottom terminal of diagnostic connector #1 for good ground connections. Repair as necessary. If no wiring or power supply problems are found, and ECU still won't enter output check mode, then ECU is faulty.