I have a 1995 Protege and it runs fine but the engine light came on, it has fault code P1794, Goodyear replaced the distributor twice and did not make the light go away, Mazda could not tell me what wrong with the car.
I subscribed Alldata and trouble shot to the ECU, according to them I have a bad computer. Howcan this be if my car is running fine ?
Where is the computer located ? and how to replace it ?

Thanks

 

There is somewhat of a discrepency in the manual about this but basically the PCM is not being continually supplied battery voltage to either pin 4B or 4I. Question. Is the 15A 'Room' fuse OK or do you have any problems with it either blowing intermittently or loosing interior light, clock, radio?

 

Thanks for replying Babyhue

I checked the room fuse (15A) and it's ok, do you know where the computer is located on the car ? and what's are steps on how to replace it ?

Thanks again

 

The computer is located on the floor "hump" of the car. It is directly in front of the radio mounted to the floor on a bracket. You must first remove the e-brake cover housing, then the gear shift plastic housing and then you will see it . All you need is a phillips screwdriver and a 10mm socket.

If you must replace it, this ECU is a year model specific to 95 (I know...been there, done that) and depends if your car is auto or standard.

 

The ECU is located just below the ashtray and in front of the shifter. You will need to remove the rear console between the seats as well as the front console that surrounds the shifter as bkey noted. Won't be able to miss it once those trims are removed. There are no steps other than just unbolting it and replaceing.
The reason that I noted a discrepency in the manuals is that in the 95 manual for diagnose of 1794 there is a difference in which power supply source is not constantly applied. For the Z5 engine it lists PCM pin 4B as being the one that is loosing the batt voltage. BP engine however list the 4I pin as fault area in the possible cause part but then has you checking 4B with no further checks at pin 4I.
96 MY lists pin 9I as faulty pin voltage location in both engines. In explanation, pin 4B in both years is a voltage signal input from the main relay once the engine is running. Pin 4I is a continuous voltage input at all time thru the 15A room fuse. I am assuming that the factory manual is incorrect for 95 MY. What did your troubleshooting from Alldata have you checking.
If just that a poor/loose connection is causing the same problem, would sure hate to see you go thru the trouble and expense of installing another PCM, either new or used, and have the same problem back again. Some things we could look at further if you are interested.
p.s. the 4B wire is White w/ Red stripe, 4I is Blue w/ Red stripe.

 

Thanks for helping guys. Goodyear told me they check 4B and the voltage is ok. According to Alldata troubleshoot chart, if the voltage at 4B is ok then replace the PCM(computer)
I will double check this and get back.

Thanks again

 

I replaced the computer I purchased from Rockauto for $100, the engine light is off now but it has a fault code P1000.
The car is still running fine. Fault code 1000 is Readiness Function code according to Alldata info. I think I got another bad computer, what do you guys think ?

Thanks again.

 

P1000 only means that the system monitors have not been completed. The computer needs time to be able to run the following system self checks: EGR , O2 sensor and heater operation, Catalyst efficiency, and evaporative emissions checks. Car just needs to be driven untill all of these self tests have been run and then if all of them pass the P1000 will self clear. Hope that light stays off for you.

 

Again thanks Babyhuey, you know so much about Mazda cars.
I will put it together and drive it for a few days and check the code again.

Thanks
Salamat
Gracius
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