Instructions for EEC-IV systems

Original guide and pictures by Joshua Langevin. Reposted from the SHO Phoenix Project and subtly edited by Devin Fisher

This is a step by step guide to checking the engine trouble codes in your SHO. Remember that just because your CEL (Check Engine Light) isn't on does not mean that there are no codes stored by your computer. If you are having troubles with your SHO, this is the first place you want to go.

There are three tests, KOEO (Key On Engine Off), KOER (Key On Engine Running), and the Cylinder Balance Test.

KOEO (Key on engine off)

Make sure the engine is warmed up to normal temperature. The car should be in neutral, parking brake set. Shut the heater/AC off. There is a test harness located on the passenger side of the engine bay, directly in front of the firewall. These plugs may be inserted into a protective cover that you must remove.

Computer test harness
Fig. 1 - Location of the computer test harness

Now use a jumper wire and connect the upper-right pin on the black plug with the large pin in the grey plug, like so. A paperclip seems to be a popular choice.

Jumper configuration for test harness
Fig. 2 - Installing a jumper into the test harness

For a better look at where this jumper wire goes, look at this diagram. Connect the jumper to the red dot on the connectors.

Jumper configuration diagram
Fig. 3 - Jumper configuration diagram

Now jump into the car, and make sure you have a pad and pencil ready to jot down the codes. Now turn the key to "On", but do not start the car. You will see the CEL blink and should hear the cooling fan and fuel pump cycling. Then the codes will start being displayed.

The codes are displayed by the CEL in flashes separated by pauses. If you have a Gen I (89-91) there will be two sets of flashes, if you have a Gen II (92-95) there will be three sets. As an example, a code of 256 would look like this:

2 P 5 P 6
*flash*flash* PAUSE *flash*flash*flash*flash*flash* PAUSE *flash*flash*flash*flash*flash*flash*

The common code 114 would look something like this

Example of a flashing CEL
Fig. 4 - Example of a flashing CEL. This animation will repeat every few seconds

It can be a little confusing at first, but the car will display the codes twice. Then it will flash once, and then move on to the stored codes. These are the codes that have been stored by the computer but may or may not have found when testing.

KOER (Key on engine running)

To obtain the running codes start the engine. The CEL will blink 3 times. Watch the RPM gauge carefully, and when you see the RPMs rising (which is the computer advancing the timing) then follow these steps:

  1. Turn the steering wheel a half turn to the right and then a full turn to the left
  2. Step on the brake
  3. If your car is an ATX, switch the overdrive off, then back on

In a moment the RPMs will go back down and the check engine light will flash once. Now step on the gas for just a second (at least 1/4 way down). The codes will appear shortly, whether or not the steps previous were performed properly. If they are not, you may get erroneous codes in regards to the test input that was not done properly. Doing this process several times can help pinpoint whether there is a problem or if some steps were not performed correctly.

Clearing the Engine Codes

Generally, the best way to clear your codes is to disconnect your battery for at least 10 minutes.

Cylinder Balance Test

This is to make sure that all of your cylinders are working right. After you have run the KOER tests, press the gas pedal down again at least 1/2 way, just for a second. The tachometer needle will move and the engine will start running a little rough. This is because your computer shut one of the cylinders off. It will do this a total of six times, once for each cylinder. Then it will display the codes.

Code Description
10 Problem with cylinder 1
20 Problem with cylinder 2
30 Problem with cylinder 3
40 Problem with cylinder 4
50 Problem with cylinder 5
60 Problem with cylinder 6
9 No Problems