89-91 CPU Trouble Codes

(Mirrored from original URL:  http://www.johnr.com/cpucodes.html       --RETed)

This page explains information about retrieving and clearing the CPU trouble codes for the RX-7 Engine Computer (ECU) for 89-91 models. If you have an 86-88 model, try the TeamFC3S (Turbo II) Error Codes page. I've been told the actual codes are the same for the Mazda 929 (and possibly others?) from 89-91 as well, though I'm sure the technique to retrieve them is different.

Getting the engine codes from a 1989-1991 RX-7.


Getting the codes

  1. You need to turn the engine off, and remove the key.
  2. Now you need to pop the hood and locate the green "test" connector(s). These connectors are located in the front of the car, near the battery on the driver side, and near the airbox on the passenger side. They are green, and not connected to anything.
  3. Locate the green, SINGLE connector near the battery. It should be close to another green multi-socket connector. Take a jumper wire (anything is fine, old speaker wire, etc.) and cram one end into the single green connector, and ground the other end. (I find the conveniently located (-) battery post usually does the trick)
  4. Get back in the driver's seat, and turn the key to the IGNITION only. DO NOT START THE CAR.
  5. The Check Engine Light should come on (as usual when you hit ignition with no start), and then go out. It will then start flashing the CPU version of Morse Code. (See below for decoding hints.)
  6. Watch carefully. Get the timing down. Note that SEVERAL trouble codes my be reported on. You can leave the key in as long as necessary, the codes will continue to repeat indefinately.
  7. Once you have the code(s), you can remove the key, remove the jumper, and start figuring out what is causing the code(s).
  8. Its THAT simple. If you make repairs and want to "clear" the code - to see if you actually fixed things - you should remove the (-) battery cable for about 30 seconds. Repeat steps 3-7 above BEFORE starting the engine to make sure you cleared the code(s). Then take a test drive and repeat steps 1-7 again to see if your problem is gone.

Reading the Codes

    The codes are displayed from lowest to highest, tens digit first, the one(s) digit. A sample reading (with trouble codes 9 and 24) is below. S - short (1/2 sec), L - long (1 sec), P - Pause (2 secs, pause between codes. There is a "double-pause" before the sequence repeats). If you had trouble codes 9 and 24, you would see: ... SSSSSSSSS (9) P LLSSSS (24) P P SSSSSSSSS (9) P LLSSSS (24) P P ... (repeat forever) I find it easiest to try to determine what the codes are first, then "predict" the pattern of blinks. This is a good way to confirm you have the codes correct.

What causes the codes/Check Engine Light

    Whenever the CPU gets an "input" from one of its sensors that is out of a pre-determined range, the Check Engine light will come on. This light means that the CPU is essentially "ignoring" the input from a specific input device (or devices) and using "fall-back" values that are pre-programmed into the CPU. For example, if the throttle position sensor (TPS) says the throttle is closed, but the airflow meter says you are using a lot of air, the CPU will mark the TPS suspect, ignore it, and use a default value for it. As soon as the input looks reasonable again, the CPU will go back to using that input. The Check engine light will go out, but the trouble code will be saved.

    Some dealers will try to tell you there is not a problem if the check engine light is off. This is simply not true. They can easily retrieve the codes. I suggest you stay far away from Mazda dealers, and find a trusted independant mechanic, but I digress...

So, I've got a code, what does it mean?

    See below for the exact meaning according to the Shop Manual. Read on for actually interpreting that code... Note that if you get multiple codes, there may really only be ONE thing wrong. Much of the system interacts with several components, so a single failure may "cascade" into multiple troubles. Use your brain (or a trusted mechanic) to determine the most likely cause of the problem. It is doubtful, for example, that your Intake air sensor, altitude compensation sensor, intake airflow meter, and TPS are all bad. Its more likely you have a loose electircal connection and a vacuum leak. The components are quite reliable, so always suspect the simple solution first. It is normally the cheapest as well. (A vacuum hose is pennies, but a TPS is hundreds of dollars.)

The Codes - from the 1990 Service Manual (86-88 do NOT match!)

    Code - Input Device - Fail-safe operation mode

    Code - Output Device