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How To Diagnose A Check Engine Light (CEL)


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#1
snailman153624

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IMPORTANT: THIS INFORMATION ONLY APPLIES TO V6 MODELS (KL-03 Engine)

The Check Engine Light is sometimes caused by "accident." Or, one error will eventually cause another (cause/effect). It is recommended that you RESET your ECU after performing the diagnostic, and after a few days of driving (if the CEL comes on again), perform the diagnostic again. Instructions for resetting the ECU are below (3rd post).



DEFINITIONS:

OBD-I - "On Board Diagnostics" revision 1; this is for the 93-95 model 626/MX-6/Probe GT

OBD-II - "On Board Diagnostics" revision 2; this is for all 96+ model 626/MX-6/Probe GT; if this is you, you cannot diagnose the check engine light without a scan tool. However, you CAN take your car to an AutoZone for a FREE diagnostic B)

ECU - Engine Control Unit; this is the car's computer, it manages your engine, and lets you know when there is a problem

CEL - Check Engine Light; it is the squiggly looking box that glows orange on your dashboard when your engine is experiencing a malfunction that the ECU (car's computer) can detect

Trouble Code - A number stored in the ECU which can be referenced in a table (listed below) to determine the cause of the CEL (Check Engine Light).

Diagnostic Module - (OBD-I only) This is a little black enclosure under your hood directly in front of your fuse panel, about 2" x 3" (4 cm x 6 cm)

IAC Valve - Idle Air Control Valve; this regulates the amount of air your engine gets at idle to maintain a steady idle speed.

VRIS - Variable Resonance Induction System; this is a feature that your car uses to naturally supercharge the engine, improving the engine power at lower RPMs. The system works with the ECU, and opens/closes two butterfly valves on the Intake Manifold to vary its length at various RPMs, or commonly called "VRIS Points." It has two vacuum solenoids controlling two vacuum actuators, which in turn pull a lever to open or close the butterfly valves.



FOR OBD-II (96+) 626/MX-6/Probe GT:

Note: If you do not have a scantool, you cannot complete this procedure. AutoZone will do the diagnostic for free, or you can purchase a scantool there or any other parts store.

1 - Locate your OBD-II connector. It is on the driver's kick panel (by the foot of the door) and has a little door with the word "OBD-II" on it.

2 - Connect the scantool per the instructions that came with it; the Trouble Codes will be displayed on the screen of the scantool.



FOR OBD-I (93-95) 626/MX-6/Probe GT:

1 - Open the Diagnostic Module, and in the lid that flips open is a chart that tells you what each pin (the little connectors) is. You need to locate the pin labeled "TEN" and another labeled "GND." Using a paperclip or a piece of wire, connect, or "jumper" these two pins together. Some people have reported that their "GND" pin does not exist (has no connector, just an empty hole); this is ok, "GND" stands for "ground." If you DO NOT have a "GND" pin, then simply connect the "TEN" pin to the negative terminal of your battery (a.k.a. ground).

2 - Put your key in the ignition, but do not start your car. Turn the key into the "ON" position. Your Check Engine Light should turn on momentarily (a few seconds) and then turn off. Then, it will start flashing a certain number of times. A LONG flash indicates a "10" and a short flash indicates a "1." You add them together to determine the Trouble Code.

So, for example, 2 long flashes followed by 3 short ones would equal "10 + 10 + 1 + 1 + 1" which is 23. There is a pause between error codes, and it repeats the codes over and over until you turn the key off.

3 - See "Some Additional Info" below for optional steps.

4 - Remove the key from the ignition, and remove the wire/paperclip from the Diagnostic Module. You have successfully retrieved the Trouble Codes.




SOME ADDITIONAL INFO FOR OBD-I SYSTEMS:

At this point, you can also start the car and adjust the base idle and base timing. The car is in diagnostic mode, and will ignore most sensor data, and will bypass the IAC Valve. This allows you to make several other adjustments as well. For more information on how to perform these procedures, consult a repair manual.



You can also test the functionality of the VRIS solenoids and actuators at this point. In order for this test to work, you will need a helper (to observe), and the engine must be warmed up. There must also be sufficient vacuum left in the vacuum canister. You can ensure the engine is warmed up and has vacuum by letting it idle (until it is at operating temperature) prior to proceeding.

Once this is done, turn the engine off, and connect the "TEN" and "GND" pins as described above. Have an observer watch the VRIS actuators while you turn the key to the "ON" position. They should BOTH momentarily open, and then close. If only one opens, or none of them do, you will need to further troubleshoot/repair the VRIS system. Consult a repair manual for detailed instructions.

#2
snailman153624

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NOTE: THIS IS A LISTING OF OBD-I CODES ONLY AND ARE NOT INTERCHANGEABLE WITH OBD-II

"RH02S" and "LH02S" stand for "Right Hand/Left Hand Oxygen/02 Sensor" where left hand is the front of the engine, right hand is the rear of the engine.


Code----Circuit Diagnosed------------------------------Memorized?
02--------'NE2' crankshaft position sensor----------------Yes
03--------'G' camshaft position sensor---------------------Yes
04--------'NE1' camshaft/crankshaft position sensor----Yes
05--------Knock sensor----------------------------------------Yes
08--------Volume Air Flow sensor (VAF)--------------------Yes
09--------Coolant temperature sensor (CTS)-------------Yes
10--------Intake air temperature sensor (IAT)------------Yes
12--------Throttle position sensor (TPS)--------------------Yes
14--------Barometric pressure sensor----------------------Yes
15--------LHO2S inactivation error--------------------------Yes
16--------Exhaust gas recirculation (EGR) system--------Yes
17--------LHO2S inversion error------------------------------Yes
23--------RHO2S inactivation error---------------------------Yes
24--------RHO2S inversion error------------------------------Yes
25--------Fuel pressure regulator control solenoid-------Yes
26--------Canister purge solenoid----------------------------No
28--------EGR vacuum solenoid-------------------------------No
29--------EGR vent solenoid-----------------------------------No
34--------Idle air control (IAC) solenoid---------------------No
41--------VRIS #1 solenoid------------------------------------No
46--------VRIS #2 solenoid------------------------------------No
67--------LFAN relay (1993 only)-----------------------------No
69--------ECTF sensor (1993 only)---------------------------Yes


I obtained this list from the site below. They also have the FS series engine trouble codes for those of you that have the 4 cylinder models. They also include instructions on retrieving them if the above instructions do not apply to you, or if you are having a hard time understanding them.

Lastly, they give a good description of many of the trouble codes, and how to fix them:

http://homepage.ntlw...lf/malfcode.htm
backup link: Attached File  1993-1995 Engine Controller Malfunction Codes.pdf   429.79KB   453 downloads
Here are some other VERY USEFUL links:

http://homepage.ntlw...adbury/probemx/

http://homepage.ntlw...obemx/p_m19.htm

Edited by NDM, 31 July 2012 - 11:38 PM.

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#3
snailman153624

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HOW TO RESET THE ECU:

There are two methods for resetting the ECU. The first involves disconnecting the battery, so any settings you have (clock, radio, etc.) will be lost, and if there is a security code on your radio, it will be activated. The second (preferred) method does not affect anything, and requires no tools. After completing either one of these, START THE CAR and let it idle for AT LEAST 3 MINUTES without touching the gas. Then, you can drive as normal. You may notice a slight hesitation in the car, it is simply relearning how the engine responds, as well as your driving habits.

Method 1: Simply remove the negative battery terminal, and hold the brake pedal in for at least 30 seconds. (NOTE: The SOLE purpose of holding the brake pedal in is to drain any residual power from the electrical system, allowing the computer to reset itself). Then, reattach the negative battery terminal.

Method 2: Remove your center console (the trim piece around the shift knob). The ECU is located directly underneath/behind the radio and ashtray underneath this trim piece. This does not require any tools (on most models) since the piece just pops up. Then, simply unplug ALL of the wiring harnesses that plug into the ECU (it is a gray metal box with a yellow plastic connector on it) and leave it unplugged for a few minutes. Then, simply plug them back in.


You have successfully reset your ECU B)

#4
blackshine007

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Nerd :P

#5
yabaguymia

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I really need to check whats wrong with my car since the CEl is on but i dont know the security code for my radio. where can i find out what it is??

#6
playboyinsac

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snailman........your in to the 6 to much and i think that if u keep spending time on it like u are your brain will give..lol :rolleyes: (good info though thanks)
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#7
snailman153624

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snailman........your in to the 6 to much and i think that if u keep spending time on it like u are your brain will give..lol :rolleyes: (good info though thanks)

I'm an engineer. You gimme a problem, I will solve it, no matter what it takes :lol:

Not just the car, I'm like that about everything, when something strikes my curiousity, I learn as much as I can about it.
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#8
Zuke626

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I really need to check whats wrong with my car since the CEl is on but i dont know the security code for my radio. where can i find out what it is??

If its not with your owners manual you have to get it at the dealer.

#9
snailman153624

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I really need to check whats wrong with my car since the CEl is on but i dont know the security code for my radio. where can i find out what it is??

If its not with your owners manual you have to get it at the dealer.

I think on the pre-'98 models I read in the manual there is a way for it to show you the security code if you push certain buttons on the radio. I remember I did this before I pulled out the factory radio to put in my aftermarket H/U. Who woulda thought, "0 0 0 0" :lol:

#10
Zuke626

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HOW TO RESET THE ECU:

There are two methods for resetting the ECU. The first involves disconnecting the battery, so any settings you have (clock, radio, etc.) will be lost, and if there is a security code on your radio, it will be activated. The second (preferred) method does not affect anything, and requires no tools. After completing either one of these, START THE CAR and let it idle for AT LEAST 3 MINUTES without touching the gas. Then, you can drive as normal. You may notice a slight hesitation in the car, it is simply relearning how the engine responds, as well as your driving habits.

Method 1: Simply remove the negative battery terminal, and hold the brake pedal in for at least 30 seconds. (NOTE: The SOLE purpose of holding the brake pedal in is to drain any residual power from the electrical system, allowing the computer to reset itself). Then, reattach the negative battery terminal.

Method 2: Remove your center console (the trim piece around the shift knob). The ECU is located directly underneath/behind the radio and ashtray underneath this trim piece. This does not require any tools (on most models) since the piece just pops up. Then, simply unplug ALL of the wiring harnesses that plug into the ECU (it is a gray metal box with a yellow plastic connector on it) and leave it unplugged for a few minutes. Then, simply plug them back in.


You have successfully reset your ECU B)

Heres a little bit more info on resetting the ECU without disconnecting the battery. For those worried about having to reprogram everything. CLICK

#11
Bigjames02

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Ok this may be a dumb question but why would you want to reset your ECU besides trying to get a check engine light off? Does the ecu cause the engine to perform as the driver normally drives? Would i notice a gain in performance if i reset the ecu? Just wondering... :huh:

#12
snailman153624

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Ok this may be a dumb question but why would you want to reset your ECU besides trying to get a check engine light off? Does the ecu cause the engine to perform as the driver normally drives? Would i notice a gain in performance if i reset the ecu? Just wondering... :huh:

Yes, the ECU learns your driving habits, as well as driving conditions. If you change your intake from stock to a performance, or slap some headers on, it is a good idea to reset the ECU so it can "relearn" the new conditions.

If you just bought the car off of an 80 year old grandma who never even found the gas pedal but just cruised around in 'D' at idle then yeah, time for a reset. B)

#13
Bigjames02

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Well...lol... didnt but it from a grandma, but i got it from my dad who is "mr speed limit". That and he got it from his boss, who i'm pretty sure never sped in it either...so, i'm gonna reset it and see if it makes a difference, and get that damn check engine light off.

#14
Bigjames02

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Alright i Reset it...and then took a drive. It drives a little better and the check engine lighte is off! B) Oh, and before it used to idle weird...it would go up a little then back down with the ac on....now it stays the same. Thanks guys! B)

#15
snailman153624

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Just FYI, I updated the links towards the top [thanks NickR]. I also saved all of those pages locally in case the owner takes down their site. If you need the files they will be available on the FTP site eventually [need to add some permissions].




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