Engine Self Test 1990 3.0L V-6 Engine

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Engine Self Test 1990 3.0L V-6 Engine

Overview

1990 to 1992 Probes with 3.0L engines were equipped with an On Board Diagnostic (OBD) system to detect malfunctions in sensors and notified the driver through the Check Engine light on the instrument panel.

The 'Check Engine' light or MIL (Malfunction Indicator Light) light on the instrument cluster illuminates when the ignition is turned to the 'On' position. It will go off a second or two after the engine is started. If the light stays illuminated after the engine is started or illuminates while driving, there may be a problem with the engine. Checking for error codes is an easy way to find out what's wrong and what, if anything, caused the 'Check Engine' light to illuminate. There are two types of self tests. The first is the Key On Engine Off (KOEO) Self Test, which tests the memory and certain sensors for any fault codes. The second test is the Key On Engine Running (KOER) Self Test, which allows you to check for faults present only when the engine is running.


Procedure

There are three ways to check for error codes:

Engine Code Scanner
If you have a Super STAR II or equivalent engine code scanner, you can perform a quick test on your engine to see if there's anything wrong. Simply connect it according to the manufacturer's instructions and write down the codes that appear. Codes are listed below.

Analog Voltmeter
If you don't have an engine code scanner, you can perform the same test with a standard analog voltmeter. Set the meter to read between 0 and 15 volts. Find the OBD Self Test Connector under the hood, between the battery and the left fender. Connect the positive wire of the voltmeter to the Self-Test Output (STO) pin on the OBD Connector (see image below). Connect the negative wire to a ground.

Key On Engine Off Self Test: Start the engine and run intil it reaches the normal operating temperature. Turn the ignition switch OFF for 10 seconds, then turn the ignition switch ON, but do not start the engine. When you're ready to start the test, connect a jumper wire between the Self-Test Input (STI) connector and the Signal Return wire on the diagnostic test connector. The STI wire is a white wire with a red stripe located just behind and slightly to the right of the right strut mount.

Key On Engine Running Self Test: Start the engine and run intil it reaches the normal operating temperature. Turn the ignition switch OFF for 10 seconds, then restart the engine and allow it to idle. When you're ready to start the test, connect a jumper wire between the Self-Test Input (STI) connector and the Signal Return wire on the diagnostic test connector. The STI wire is a white wire with a red stripe located just behind and slightly to the right of the right strut mount.

The voltmeter will display a pulse for 3 seconds when the test is first started. Engine codes will appear on the display as a pulse. See below for how to interpret the pulses.

MIL Light
If you don't have an engine code scanner, the easiest way to check for error codes is by using the Malfunction Indicator light on the instrument cluster.

Key On Engine Off Self Test: Start the engine and run intil it reaches the normal operating temperature. Turn the ignition switch OFF for 10 seconds, then turn the ignition switch ON, but do not start the engine. When you're ready to start the test, connect a jumper wire between the Self-Test Input (STI) connector and the Signal Return wire on the diagnostic test connector. The STI wire is a white wire with a red stripe located just behind and slightly to the right of the right strut mount.

Key On Engine Running Self Test: Start the engine and run intil it reaches the normal operating temperature. Turn the ignition switch OFF for 10 seconds, then restart the engine and allow it to idle. When you're ready to start the test, connect a jumper wire between the Self-Test Input (STI) connector and the Signal Return wire on the diagnostic test connector. The STI wire is a white wire with a red stripe located just behind and slightly to the right of the right strut mount.

The Malfunction Indicator light will go out after a second then will flash the engine error codes, if any. See below for how to interpret the flashes.

Interpreting the Codes

The pulses on the voltmeter and the flashes on the MIL light translate into two digit codes. To simplify things, we'll call all flashes and pulses, pulses. There are two types of pulses. A long pulse is a pulse that lasts 1-1/2 seconds. A short pulse is a pulse that lasts a 1/2 second. These are pretty distinguishable. The long pulse represents the first digit of a two digit code and the short pulse represents the last digit. So, if there are three long pulses followed by four short pulses, that would be the number 34. If there isn't any long pulse, the number is less than ten. Eight short pulses with no long pulse would be an 8 code. If there is a long pulse, but no short pulse, the code is 10. If there is more than one code, each code will be separated by a 4-second pause.

Continuous Memory Codes are codes that appear while normal running and are stored by the computer for a period of time. During the Key On Engine Off Self Test, after all the codes are displayed, there will be a six second pause, a single flash, followed by another six second pause. Any Continuous Memory Codes will then be displayed in the same fashion as the regular codes. Continuous Memory Codes will only display once, before being erased, so make sure you're ready for them.

If there are no problems found, code 11 will be displayed.

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Error Codes

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