The car overheated for my son about two weeks ago. I had his older brother, who was in town visiting, drive me to where he was, drop me off and pick him up and then follow me home in the late evening hours. We wound up stopping a few times as the car reached the “HOT” level and shut it down and allowed it to cool. When we reached a construction business’s parking lot about a mile from home, I parked it there for the night to let it cool down completely. I rode home with the sons and asked my wife to take me up to the vehicle early the next morning to retrieve the car before too many employees started showing up for work.

We arrived at about 05:30 and a few cars were already in the lot around the MAZDA. I got into the car, turned it over and it started on the first shot. My wife followed me home for the mile and I parked it in the driveway and let the car run for a few minutes. I allowed it to reach normal operating temperature and then shut it down. From my multiple sessions behind the wheel, and study of the gauges and performance of the vehicle, I had a suspicion that the THERMOSTAT had failed in the “CLOSED” position. That diagnosis is consistent with the fairly rapid overheat condition in mid-March (cool) weather [without water circulation, the thermal load from the engine never makes it to the radiator to be cooled] that I had experienced. Therefore, I found a new thermostat and gasket and changed them out that morning. Upon attempts to start the car since, the car turns over but will not start. I am now attempting to diagnose the other potential "engine OVERHEAT" possibilities. I have been in the process of attempting to access collected/stored engine code data; however, locating a data access port/connector (likely OBDI information) on the vehicle has not produced any positive results. After searching online for a few weeks I have found no real help locating the diagnostic port.

Has anyone had any experience with the Diagnostic Port on the 1991 DX version of the Mazda 626? From my reading the plug configurations are varied and pin diagrams are very difficult to find. I am attaching a photo of my most probable, thus far, location of a diagnostic port configuration; however, it is highly speculative at this point in time. Any insight into this question would be helpful!

This is my only inclination as to access to diagnostic data for the 1991 Mazda 626 DX; however, the configuration doesn't really present much hope!

 



 

I would think your car is pre-OBD2 so hopefullythis video clip should help.

 

Riaan34, thank you for the great guidance! I have now searched the entire right half of the engine compartment for the Mazda Diagnostic Port [M.D.P.], even removing the air cleaner compartment, the battery base panel, and the inner plastic fender. I had considered that during the assembly process, the M.D.P. block might have never been mounted in its designated position and might be dangling in some inconspicuous cavity in the front-end. Unfortunately, that does not appear to be the case either. I'm not sure where I might go from here.

 

CharlesCrown, thank you for posting the great video; the information is awesome! I have searched the entire right half of the engine compartment for the Mazda Diagnostic Port [M.D.P.], even removing the air cleaner compartment, the battery base panel, and the inner plastic fender. I thought that maybe during the assembly process, the M.D.P. block might have never been actually mounted in its designated position and might be dangling in some inconspicuous cavity in the front-end. Unfortunately, that is not the case either. I'm uncertain where I might go from here. Old car, much rust on all fasteners. I now have several broken bolts to extract and replace; nothing like making yourself more work.

 

Your Mazda is not OBDII but dinosaur OBD1. I would be VERY CAREFUL using a paper clip method on your PCM you may fry it and then will need to replace it.

For other members please read the history of the on board diagnostic systems (OBDI OBDII and CANBus) and learn what their early short comings were on OBDI. Also there is more or less an exact year between OBD1 to OBDII and CANBus, PCM,TCM and ECUs. Knowing this can be more helpful when responding to members with pre OBDII systems.

 

Sorry I couldn't help. I have a MX5 and it's just as in the video. I have done many early Mazdas and they have all been fitted with that diagnostic box and it has always been located under the bonnet. I have only come across one where the wiring was not laid out as in that video and it's located behind the strut tower. The std testing procedure without a scantool is the same. "With the ignition off bridge the terminals labelled TEN and GND then turn the ignition on and count the flashing diagnostic light". I have done many and never fried the ECU Good luck with it.

 

Well we will just have to take your word for never firing a ECU. The sad thing is when advise on the DIY level is given on any forum it’s sad if a member trust the advise and does not have the same outcome.


As a “Golden Rule “ on forums I only give the correct service procedure as per Factory service information unless I state very clearly otherwise. And try to give a
l the downfalls to a DIY method. This includes shortcuts for doing a service as well.

I do except that in the end people will choose advise mostly with the same thought values and how a member authors a response.


It’s also funny how without knowing a ECU can be damaged without knowing by doing off the books procedures and then a few weeks or even months go by and then the ECU fails.

 

I'm sure you mean fried an ECU.

 

I should give you important information to think about in the future... on ALL forums grammar ***** are look down on by members and generally are not tolerated by the Administrator's and or Moderators for obvious reasons. Keep that in mind when responding with correcting authored responses.

Grammar **** - Wikipedia
Grammar **** (also known as Grammar Pedant, or Spelling ****/Pedant) is an informal, pejorative term used to describe someone who regularly corrects or criticizes minor errors in spelling, grammar, and punctuation in speech and writing