You do not need a scanner (but it is alot easier.) Here is how to do it with a wire or amp meter:




Before starting, make sure the key is out of the ignition and there is no electrical load on the car.



This is a picture of the two plugs you will use to run the diagnostic test. These plugs are both mounted on the passenger side firewall shroud. The are plugged into a cap that says "EEC Test" on it. You will need to remove the plugs from this cap.

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From there you want to take a short piece of wire (or a paperclip) and plug one end into the upper right contact on the large plug and the other end into the contact of the small plug. From here, go and sit in the car.

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Key On Engine Off



With pen and paper in hand, turn the ignition to the "on" position, but do not start the car. The "check engine" light will blink very quickly for about a second and then shut off. You will hear the cooling fan turn on and then off as well as the fuel pump. After this, the codes will start being emitted from the "check engine" light. The codes are displayed in pulses in sets of 3. For instance, a code 114 would show as follows:

Flash *1 second pause* Flash *1 second pause* Flash Flash Flash Flash

(Note to 1989 - 1991 SHO owners: Your codes will display the same way, but are two digits rather than three)

After the computer has displayed all the codes, it will repeat them all again. After that, there will be a single flash and then the computer will start displaying the stored codes. The stored codes are problems that the car has noticed in the past, but didn't necessarily notice when testing itself. The codes will be displayed in the same way as the first set.

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Key on Engine Running

After all the engine off codes have been displayed, turn the car on. The "Check Engine" light will blink 3 times to indicate that it is a V6 engine (blinks for half the amount of cylinders). After this, you will notice the RPMs rising. This is the computer advancing the timing. While the car is doing this you must do the following:

• Turn the steering wheel one half turn in each direction
• Tap the brake pedal once
• (ATX) Press the overdrive switch once to turn over drive off and once again to turn it back on

Doing this lets the computer know that these devices are all working properly and avoids wasting time with false alarm codes.

When the RPMs drop back down to normal the check engine light will flash once. When this happens you want to "goose" the throttle (at least 25%) and then let up. After you do this your codes will be displayed.

Codes are displayed in the same fashion they are displayed when the engine is off.

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Additional Tests

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There are a couple more tests that you can run during the self test procedure.

Cylinder Balance Test

The first is the cylinder balance test. This test ensures that all cylinders are operating properly by measuring the RPM drop when a cylinder is "removed". This is done by removing spark. You can activate this test during the "Key on Engine On" test. After all the codes have output, give the car about 50% throttle and then let off. You will notice the RPMs go up and then come down slightly. The engine will also sound a little rough when the RPMs drop. This is the sound of your engine running on 5 cylinders. The RPM fluctuation will repeat 5 more times.

When the test is done and the RPMs go back down the "Check Engine" light will flash to indicate if it found any problems. Here is a break down of the codes:

• 10 - Number 1 cylinder balance problem
• 20 - Number 2 cylinder balance problem
• 30 - Number 3 cylinder balance problem
• 40 - Number 4 cylinder balance problem
• 50 - Number 5 cylinder balance problem
• 60 - Number 6 cylinder balance problem
• 9 - No problems found

Solenoid/ Relay test

This test cycles all your relays and solenoids (except starter) so that you can check for proper operation. To initiate the test, run the "Key On Engine Off" test and wait until all the codes have been displayed. After all the codes have been displayed, press the the throttle down half way. This initiates the test. Now every time you blip the throttle the solenoids will the cycle. The "check engine" light will also cycle to let you know that you are doing this right.



Also tossing a can of Berrymans B-12 or Seafoam in the gas tank wouldn't hurt either.