1G Diagnostic testing without a scantool (CEL testing) ~ 1g Turbo models

Is your 1g throwing a check engine light? Here is a simple way to diagnose it without the use of a scantool or diagnostic checker.

All you will need is a simple voltmeter. First, locate the OBD (Is right next to the fuse box near the driver's feet).

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Take off the black cover. Turn the ignition to "ON" to turn the electrical on. Wait 5 seconds until connecting the pos/neg voltmeter terminals. Connect the positive wire of the voltmeter to pin 1 (upper left pin) and the negative to pin 12 (lower right pin).

Here is a pin layout of the port.

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The needle on the voltmeter should make a series of "sweeps". It should consist of a certain number of long sweeps followed by a number of short sweeps. Make sure you watch what the needle does. For example, one long sweep followed by three quick sweeps equals "13". Then, you take that code and look up what code that is diagnosing. Here is the list:

For 90-92 turbos:

1. ECU
11. Oxygen sensor
12. Air flow sensor (MAF)
13. Intake Air Temp sensor
14. TPS
21. Engine Coolant Temp sensor
22. Crank Angle Sensor
23. TDC sensor (cylinders 1 and 4)
24. Vehicle Speed Sensor
25. Barometric Pressure sensor
31. Detonation sensor (Knock Sensor)
41. Injector(s)
42. Fuel pump
43. EGR
44. Ignition coil
9. Normal state


For 93-94 turbos:

1. ECU
11. Heated oxygen sensor
12. Volume air flow sensor (MAF)
13. Intake Air Temp sensor
14. TPS
21. Engine Coolant Temp sensor
22. Crankshaft Position Sensor
23. Camshaft Position Sensor
24. Vehicle Speed Sensor
25. Barometric Pressure sensor
31. Detonation sensor (Knock Sensor)
41. Injector(s)
42. Fuel pump
43. EGR
44. Ignition coil or transistor
9. Normal state

NOTE/EDIT: This can also be done with a digital voltmeter. A short sweep is going to be less than 1v while a long sweep will be around 14v.

Keep in mind that this can be done with non-turbos. I specifically posted towards 1g turbos because I don't have non-turbo codes.

Feel free to email me with comments or questions.
Thanks, Jim

 

[Ninety-3_laser]

Is your 1g throwing a check engine light? Here is a simple way to diagnose it without the use of a scantool or diagnostic checker.

All you will need is a simple voltmeter.

So I have tried this with my test light. Will that not work? Also, is there an easier platform to have a conversation? Like Facebook?

 

[19Eclipse90]

Also refer to 1G Code Reader - CEL Code Reader for other options.

This was a technical service bulletin put out for these cars back in 1992.

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[Ninety-3_laser]

So, since it's already been done, what now? Should I try an LED? See if it still works?
Would I have any other issues from doing this?

 

[19Eclipse90]

You tried it with the test light. I assume you initially asked because it didn’t provide anything.

Does the CEL come on when you turn the key to ON position? Does it turn off after 5 seconds or remain lit?

If it remains lit, choose a different method to try reading the codes, either a voltmeter, LED, or fab up a piezoelectric buzzer.

If it doesn’t light at all, check / test the MFI fuse on the positive battery terminal. If good, pull the ECU and inspect for damage.

 

[Ninety-3_laser]

You tried it with the test light. I assume you initially asked because it didn’t provide anything.

Does the CEL come on when you turn the key to ON position? Does it turn off after 5 seconds or remain lit?

If it remains lit, choose a different method to try reading the codes, either a voltmeter, LED, or fab up a piezoelectric buzzer.

If it doesn’t light at all, check / test the MFI fuse on the positive battery terminal. If good, pull the ECU and inspect for damage.

It lights and stays lit. I do have LEDs that I can use, but no resistors to use. I guess I'll be checking out the ECU tomorrow or maybe Monday

 

[19Eclipse90]

Since the CEL lights, you should focus on reading the codes somehow. Do you know what voltage the LEDs you have are? Do you have a voltmeter? Do you have alligator clips? That’s all you need.

 

[steve]

It lights and stays lit. I do have LEDs that I can use, but no resistors to use. I guess I'll be checking out the ECU tomorrow or maybe Monday

I didn't see this back in April and I know the poster has left the site.

For anyone searching, if the CEL is on 100%, not pulsing out fault codes or flashing the on/off heartbeat that it's alive, the ECU is likely dead or seriously hurt... Time to pull it and look to see what shape the board is in.