12 posts in this topic

Diagnostic Systems for the 1993-1995 Mazda 626
MECS-II (1981-1995) All Models (except 93-95 2.0L automatics)
EEC-IV (1993-1995) 2.0L Automatics Only
OBD-II (1996-2002) All Models (Nothing in this topic applies to you, get an OBD-II code scanner)

This article covers both MECS-II (OBD-I) & EEC-IV diagnostics for 1993-1995 Mazda 626, Mazda MX-6, Ford Probe, and other vehicles.
You will need to figure out if you have either MECS-II or EEC-IV to get the most out of this article.

Short history of OBD-I diagnostic systems:
OBD-I is a generic term given to any diagnostic system prior to 1996's introduction of OBD-II.
OBD-I is a blanket term and not an industry standard set of codes like we see with OBD-II. MECS-II is considered OBD-I, EEC-IV is also considered OBD-I. which is why we have to specify the difference in methods. Just because your car is OBD-I doesn't mean you'll use the same diagnostic system as an OBD-I BMW, Toyota, or Honda. Each manufacturer had their own OBD-I system. Mazda used MECS-II and Ford's EEC-IV system.

Error codes are deciphered through a series of blinking check engine light (CEL) also known as a malfunction indicator lamp (MIL). It is comparable to morse code coming from the check engine light while the car is in diagnostic mode. Both EEC-IV and MECS-II can be checked using your engine's CEL/MIL light with exception to some 1993 versions that might not have a check engine light. If you do not have a check engine light you will need to hook up a test lamp in order to see your CEL/MIL codes. EEC-IV cars have the added advantage of using EEC-IV code scanners such as the Equus 3143 or 3145.

2 people like this

Share this post

Link to post
Share on other sites

MECS-II (OBD-I) Diagnostics
1993-1995 Mazda MX-6/626/Ford Probe (2.0L MTX & 2.5L ATX or MTX)
Source: http://homepage.ntlw...nt.htm#malfsrso
Source: http://www.scpoc.com...ntMod/codes.htm


USA MECS-II Diagnostic Connector

To enter the car into diagnostic mode for MCU or MECS-II you must jumper pins C (TEN) and E (GND).  However if that does not work (as might be the case on European versions) then try to jumper pin C (TEN) to the negative battery terminal.




European MECS-II Diagnostic Connector










To learn about the steps after getting your car into diagnostic mode for MECSII equipped vehicles please read Snailman's guide.

A = FEN = trouble code output (engine control computer)
B = MEN = switch monitor output (engine control computer)
C = TEN = diagnostic-mode input (engine control computer)
D = +B = switched battery voltage
E = GND = ground
F = FAT = trouble code output (automatic transmission control computer)
G = FBS = trouble code output (anti-lock brakes (ABS) control computer)
H = FAC = trouble code output (? not documented for North American vehicles)
J = FWS = trouble code output (? not documented for North American vehicles)
K = FSC = trouble code output (cruise (speed) control computer)
L = - = not used
M = TAT = diagnostic-mode input (automatic transmission control computer)
N = TBS = diagnostic-mode input (anti-lock brakes (ABS) control computer)
P = TAC = diagnostic-mode input (? not documented for North American vehicles)
Q = TWS = diagnostic-mode input (? not documented for North American vehicles)
R = TSC = diagnostic-mode input (cruise (speed) control computer)
S = - = not used
T = FAB = trouble code output (air-bag diagnostic monitor computer)
U = IG- = igniter coil output (for connection to external tachometer)
V = GND = ground
W = TFA = diagnostic-mode input (? not documented for North American vehicles)
X = F/P = fuel pump relay coil (ground to activate fuel pump)
Y = TAB = horn relay
Z = - = not used
3 = - = not used

MECS-II (CEL) Check Engine Light codes
These are the main check engine light codes for MECS-II 626's. You put the car into diagnostic mode by using a jumper wire between the C (TEN) & E (GROUND) pins of the diagnostic box under the hood of your car.

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

(HOLD) Automatic Transmission (ATX) Malfunction codes
Automatic transmission codes can be read by connecting the TAT and GND pins (see above for the location of this pin) and watching the "hold" light on the instrument cluster. The codes are read exactly as they are when reading the engine codes, except that the Hold light flashes, not the Check Engine Light. A summary of the codes and the reasons:

01 = NE1 (crankshaft position sensor)
06 = Vehicle speed sensor
12 = Throttle position sensor
14 = BARO sensor (located within PCME)
55 = Vehicle speed pulse generator
56 = ATF thermosensor
57 = Reduce torque signal 1
58 = Reduce torque signal 2
59 = Torque reduced/ECT sensor
60 = 1-2 shift solenoid valve
61 = 2-3 shift solenoid valve
62 = 3-4 shift solenoid valve
63 = converter lock-up solenoid valve
64 = 3-2 timing solenoid valve
65 = converter lock-up valve
66 = line pressure solenoid valve

(ABS) Anti-Lock Braking System Malfunction codes
Anti-lock braking (ABS) system codes are read when the TBS and GND pins are connected in the Diagnostic connector (see above). The codes are read, again, like the engine codes, but now on the ABS light on the instrument cluster. A summary of codes and the reasons:

11 = Right front wheel speed sensor or rotor
12 = Left front wheel speed sensor or rotor
13 = Right rear wheel speed sensor or rotor
14 = Left rear wheel speed sensor or rotor
15 = Wheel speed sensor
22 = Hydraulic unit harness
51 = Fail-safe relay
53 = Motor or motor relay
61 = ABS control unit

(SRS) Supplemental Restraint System Malfunction codes
The supplemental restraint (SRS), more commonly known as the "air bag" system will flash the highest priority code on the air-bag lamp on the dash with no need for any pin in the Diagnostic box to be grounded. The codes are read, again, like the engine codes, but now on the Air Bag light on the instrument cluster. A summary of codes and the reasons (NOTE: these are from a 1993 Ford Service Manual. Later models with dual airbags (1994+) may have additional codes not covered here. Email me if you encounter one. Also, I hope but am unsure if these apply to the MX-6...):

In order of priority from highest to lowest:
- = No air bag lamp: diagnostic monitor (DM), ignition power or bulb circuit
- = Continuous lamp: DM disconnected or inoperative
12 = Low battery voltage
13 = Air bag circuit or crash sensor shorted to ground
21 = Safing sensor mounted incorrectly
22 = Safing sensor: output shorted to battery voltage
23 = Safing sensor input feed or return circuit open
24 = Open in circuit 944B or low-resistance in crash sensor(s)
32 = Driver's side air-bag / safing sensor: high resistance or open
33 = Pin 7 not grounded at DM
34 = Driver's side air-bag / safing sensor: low resistance or shorted
35 = Low resistance across pins 8 and 9 of DM
41 = Crash sensor circuit: high resistance or open
44 = RH crash sensor not mounted properly
45 = Center (radiator) crash sensor not mounted properly
46 = LH crash sensor not mounted properly
51 = DM internal fuse: blown and short to ground no longer exists
52 = Backup-power supply: voltage boost fault
53 = Internal DM fault
- = Rapid continuous flashing or air-bag lamp: all crash sensors disconnected

3 people like this

Share this post

Link to post
Share on other sites

EEC-IV (OBD-I) Diagnostics

1993-1995 Mazda MX-6/626/Ford Probe (2.0L Automatic's Only)

Source: http://www.corral.ne...okoer.html#koeo

If you have a 1993-1995 automatic there's a good chance your car uses EEC-IV (including MX-6 and Ford Probe). There are code scanners available for EEC-IV diagnostics.

Innova Equus 3143 (no LCD) - This is basically a test lamp that you plug into the EEC-IV trapezoidal port. It's just a blinking LED, that's it, nothing more. Your check engine light does the same thing. If you have a 1993 without a check engine light just use a test lamp. The 3143 is fairly useless because a $5 test lamp does the same exact thing.

Innova Equus 3145 (LCD) - EEC-IV only scan tool. No live data. Stores code in memory, uses 2 AA batteries, can purchase a 6ft extender cable separately (recommended).

Innova Equus 3120 (LCD) - EEC-IV and OBD-II, stores codes, No live data.

Innova Equus 3140 (LCD) - EEC-IV and OBD-II, stores codes, If you have an OBD-II car this one streams live data of O2 sensor readings. Expensive but if you have EEC-IV and OBD-II cars in your driveway you might want to think about getting this.

1994 & 1995 Automatics - Find out if your car has Ford EEC-IV diagnostics.

1994 & 1995 Automatics - More Info on using EEC-IV diagnostics.

Deciphering EEC-IV codes

DaliDesign Mirror on Mazda626.net (EEC-IV Codes)

Key On Engine Off (KOEO) Testing Procedures

We have covered three separate tools in these articles used to pull codes; we will need to simplify our descriptions from here on. Whether you are using the check engine light & paper clip, test lamp, or code scanner we will simply refer to it as a "reader."

The KOEO test is actually 2 tests rolled up into 1. You'll get live fault codes and continuous memory codes. They are 2 separate streams of data both given to you during the KOEO test. During the KOEO test the EEC-IV will output codes twice during its display cycle. For instance if a code 23 and 66 were present the EEC would display 23, 23, 66, 66. The EEC will display codes in the following order:

1. Fast codes - used at the factory and are not readable by most scanners. These are displayed immediately when you start the test. It will look like erratic pulses or maybe one long pulse with different brightnesses. Just ignore it.

2. Hard Fault codes (test 1) - here comes the codes, get a pen. If everything checks out OK, you should receive a code 111. These codes will be repeated twice.

3. Pause of 6 - 9 seconds.

4. Separator Pulse - this pulse signifies the end of the Hard Fault codes.

5. Pause of 6-9 seconds.

6. Continuous Memory (KAM) codes (test 2) - any codes generated during continuous self-test will be displayed here. If everything checks out OK, you should receive a code 111. These codes will be repeated twice. Problems that the ECU has detected over multiple driving cycles are stored in continuous memory (KAM). These are probably your best bet to diagnosing continual issues.

Video Tutorial on How To Pull EEC-IV Codes

Demonstrates 3 different methods to do the KOEO test on an EEC-IV system. (jumper with check engine light, test lamp, and code reader)

Here is an example of EEC-IV output of the slow long pulse "111" Engine OK without KAM trouble codes following.

Here is an example of EEC-IV output of the slow long pulse "111" Engine OK with KAM trouble codes following. The KAM codes in this instance are 172 and 181 both of which point to an oxygen sensor fault. The O2 sensor is not included a KOEO test. If this person was to do a KOER test they would likely find the 172 and 181 codes present again. To fix this they would need to replace the O2 sensor, reset the ECU, and clear the codes.

Here is an example of EEC-IV output showing code 8 (Mass Airflow Sensor Fault) and 11 (Intake Air Temperature Fault). Notice that code 11 is actually 1 long beep followed quickly by 1 short beep. (10+1=11). A separator pulse can be easily confused with a legitimate 10+ beep. The difference being if it is immediately followed by another set of short beeps in this case it's only 1 short beep so the code equals 11.

The following instructions will walk you through the procedures for performing the EEC-IV Key On Engine Off test.

1. Make sure you have a paper and pencil ready so that you can write down any codes output by the KOEO test.

2. With your reader disconnected from the EEC-IV diagnostic port, start and run the engine until it is at normal operating temperature.

3. Shut the engine off and wait 10 seconds, then connect your reader.

4. With the engine off, and your reader connected, turn the ignition to "Run" but do not start the car. Throughout this test do not depress the throttle!

5. You will hear a few clicks and whirrs from the engine bay as solenoids are activated and sensors are tested. The reader will flash briefly as high speed codes are output by the EEC-IV. These codes are read at the factory and are not intelligible to most scanners. Ignore this flash.

6. If everything checks out OK you should receive a code "111." If not, the EEC-IV will display any errors it has received. Record these code numbers.

7. After a 6 to 9 second pause your reader should flash once, this is a separator pulse to let you know that no more KOEO codes are present.

8. After another 6 to 9 second pause your reader will begin receiving Continuous Memory Codes. If no Continuous Memory Codes are present, you should receive a code "111." If Continuous Memory Codes are present, your EEC-IV will display each code twice. Record these numbers.

9. When all codes have been downloaded turn the ignition to "OFF."

10. If you wish to perform the test again simply wait ten seconds and then go to step four.

11. Check your code readings here and correct any problems, then re-run the KOEO test before continuing on to the KOER test.

Note: If you wish to erase your Continuous Memory Codes, deactivate your reader while codes are being output during the KOEO test.

Pages of EEC-IV diagnostics can be found in Section F3 of the 1994 Factory Workshop Manual

4 people like this

Share this post

Link to post
Share on other sites

Key On Engine Running (KOER) Testing Procedures


After you have corrected any problems in the KOEO test and have passed with 111 System OK you are now ready to perform the KOER test. This test checks all sensors and engine functions while they are in their normal operating states. This test requires up to three inputs from the driver during the test. The first input requires that the brake pedal be depressed, the second requires that the steering wheel be turned at least one-half turn and then released. Finally on cars equipped with an automatic transmission, the Overdrive Off Switch (O/D) must be activated, then deactivated.

As with the KOEO test, the KOER test will repeat codes twice during its display cycle.

1. Have a paper and pen ready so you can write down any codes output by the test.

2. With your reader disconnected from the EEC-IV diagnostic port, start and run the engine at 2,000 RPM for two minutes. This is to bring the heated oxygen sensor and engine to their normal operating temperatures.

3. Shut the engine off, connect your reader, then restart the vehicle (within a reasonable amount of time as long as it's still warmed up, there's no rush).

4. Your reader will flash your Engine ID Code (it's really just a detected cylinder count divided by 2). For example, on a 2.0L Mazda 626 it will pulse two times, on a 2.5L V6 it will pulse three times. (Equus 3145 code reader correctly deciphers it for you and displays 4 for a 2.0L and 6 for a 2.5L). 

5. Make sure your steering wheel is straight prior to beginning step 5.


Immediately after you see the Engine ID Code;

Turn the steering wheel 1/2 turn (power steering input) hold it there for 3 seconds then reset the steering wheel to straight.

Depress and release the brake pedal (brake pressure input).

Lastly, cycle the overdrive switch on then off (O/D input).


Failure to do this correctly will result in many false-positive error codes such as power steering pressure out of bounds, brake vacuum signal undetected, transmission overdrive signal undetected, a couple of other error codes. You won't know which are real codes and which are false positives. It's easier with a code reader but with a check engine light pulses it's a lot of flashes (about 15-20 of them) just to get through the false codes YOU generated by not following procedure. Do it right and avoid the time and hassle of going through false error codes.


6. Dynamic Response Test (code 10 = 1 single pulse separator) for other vehicles.
On other vehicles you might see a single pulse that indicates that you should quickly go Wide Open Throttle (WOT). This test checks to verify the functionality of the Throttle Position (TP), Mass Air Flow (MAF), and Manifold Air Pressure (MAP) sensors. After a pause of 5 to 20 seconds BEFORE the KOER codes, you may receive a Dynamic Response Code (10). This will be a single pulse on your reader that indicates the EEC-IV is requesting a WOT input from you. If you detect this code, briefly depress the throttle to WOT. Failure to do so will generate an error code. In my experience so far, the Mazda 626 with EEC-IV does not request the WOT response prior to KOER codes.  So for Mazda 626 owners you can completely skip Step 6, for other vehicles owners (not Mazda 626, MX6, Probe, or Telstar) with EEC-IV that stumble upon this article in the future, step 6 might apply to you.


7. After a pause of about 4 to 15 seconds if everything checks out OK, you should receive a code "111." If not, the EEC-IV will display all trouble codes it has received.  It will first display hard faults and then continuous memory codes (KAM).  Each code will output twice. Record these code numbers or pulses. 

8. Once you have retrieved KOER codes you may turn the car off. Turn the car off with the code reader still attached. Removing the code reader (Equus tool or jumper pin) while the car is still running and in diagnostic mode will clear your codes.

9 After the codes repeat and the KOER is completed you can then perform a cylinder balance test by lightly pushing the acceleration pedal (quarter to half throttle). The cylinder balance test can take 2-5 minutes per cycle and there are 3 cycles (levels) which might be needed to properly complete that test.

10. You can repeat the test as many times as you like to check for consistency (recommend at least twice).


Some codes might share OBD-I codes but it's best to check for EEC-IV codes first.
For a list of EEC-IV codes please visit TroubleCodes.net.

Please note that vehicles prior to 1991 use 2 digit codes and 1991+ vehicles use 3 digit codes.

4 people like this

Share this post

Link to post
Share on other sites

I have an OBDII reader. How can I use it to scan the codes on my Mazda 626 1994.

Webvons, OBD-II diagnostics ports are not compatible with MECS-II (1994 MTX). Some manufacturers make conversion plugs which turn the OBD-II code scanner into an OBD-I scanner. It depends on your particular code scanner being backwards compatible with MECS-II. That's something you would need to ask your code scanner's manufacturer. Contact them.

Share this post

Link to post
Share on other sites

I wonder if someone can help me with the OBD-I code for my 1995 Mazda 626 Kronus 6-Cyl Manual.  My Check Engine light has been coming on for about 60 seconds before disappearing every so often.  It does not stay lit.  I have been to the dealership twice and they found nothing on their code readers.  They suggested that I go back when the light is on, so that they can grab a reading.  The intermittent nature of the light makes this an impossibility.  The only option was to try and grab the code while the Engine Light is lit. 


I tried to do this today, when it was lit.  I do not know if I grabbed it successfully or if it had already disappeared by the time I managed to get the jump wire into the OBD-I outlet.  I followed the instructions on how to Jump-connect the OBD-I reader and made this quick video of my Check Engine light.  (Sorry that it is sideways.)

I cannot tell what the light/code is telling me.  It seems to be two long, three short, two long, four short, three short.

Can anyone shed light on what this code is?  I think that the original cause for the light to appear had already disappeared and that this is an 'all-clear' code, but it does not seem to correspond to any of the codes listed.  Any help would be appreciated.

Share this post

Link to post
Share on other sites

Herman: those codes are: 23, 24, and 3. (My guess is that you started the video after the codes has started, because it normally flashes them in order, so it should be 3, 23, 24, then repeat.)

The 23 and 24 say you need to replace your rear Oxygen sensor (it's on the exhaust downpipe at the rear of the engine near the firewall). That's not uncommon.

The 3 suggests a problem with the cam position sensor in the distributor. But if your car is running fine that might be an old code, that got stored in memory. I would delete the codes (disconnect the battery, press the brake pedal for 10 seconds, reconnect battery) then go for a drive and see if that code comes back.

Share this post

Link to post
Share on other sites

I will do as you advise.

Thank you very much for your kind assistance.

Share this post

Link to post
Share on other sites

I replaced my muffler, but no other repairs were made.  I also did as advised:

1. Disconnected battery

2. Depressed brake pedal for 10 seconds

3. Re-connected battery

Now, there are no codes flashing at all when I engage the jump wire.  The engine light does work and can be seen when the car starts.  Shouldn't there be an 'all clear' code that flashes when no problem codes are encountered?  I thought that I read somewhere it was 111, but my memory could be failing me.

When the jump wire is engaged, should there be any flashing codes (even if no problem is detected)?

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now