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Discussion Starter #1
Mods- since this topic doesn't exist I'd appreciate it if you made this sticky. I couldn't locate anything on the net about how to check codes on a 1.8L BP engine. Additionally, the Haynes manual procedure for the 1.8L seems to be a typo and re-state the procedure used for the 1.9L SEFI engine, which is wrong. For those people looking how to check their codes on the 1.8L Mazda BP DOHC engine used in the escort GT from 91-95, here's how you do it. To perform this test, you will need a jumper wire (a paper clip works fine) and OPTIONALLY an analog, sweeping-needle voltmeter capable of reading 0-12V DC. You could also use any 12V DC device capable of showing signals in the 0.1s range and drawing total current of <200mA. An LED/resistor combo would probably work for this if you're doing it on the cheap.

  • 1. Locate the "DIAGNOSIS" connector box. It's between the battery and the firewall, is black, and about 1"x2" and has "DIAGNOSIS" written on the top. There's a clip on the firewall side of this box that must be pressed to open up the cover.

    2. Observe that written on the bottom side of the lid for this diagnostic box is a map of the pins contained within. There are many things you can do from this box, but for our purposes we are concerned with the four following pins:

    • a) FEN - stands for "flash enable". This pin grounds in sequences to produce pulses for the codes.
      b) B+ - this is a constant 12V DC pin
      c) TEN - stands for "test enable". This pin, when grounded, places the ECU into "report check engine light mode" under the KOEO (key on, engine off) condition
      d) GND - this pin is a battery ground
    3. Place engine ignition in "off position". (turn the key completely off)

    4. Use your jumper wire to connect TEN and GND together.

-- Here's a decision point: if you wish to check the CEL with an analog sweeping needle voltmeter, continue to step 6, if you wish to check it with the gauge cluster "check engine" idiot light, proceed to step 5. --

  • 5. Move key to the "on" position (KOEO). Your gauge cluster "check engine" light should start blinking a sequence. Go to step 8.

    6. Connect your voltmeter such that the positive lead is connected to the B+ pin and the negative lead is connected to the FEN (flash enable) pin. The FEN pin will pull-down the reference voltage of B+ and exactly mirror what the instrument cluster "check engine" light will flash. This is handy as it adds redundancy to the process for error checking should you have faulty instrument cluster wiring.

    7. Move the key to the "on" position (KOEO). Your voltmeter needle should begin sweeping from 0 to 12V DC (or whatever your pullup ref voltage is, if you pulled it off another source). Go to step 8.

    8. Now that you see that your instrument cluster and/or analog voltmeter needle are sweeping and/or blinking, we must interpret these pulses. This codes are reported in the following format- all codes are 2 digits in length. The first digit (tens place) is represented by a long pulse/flash (about 0.5s). The second digit (ones place) is represented by a short flash (~0.2s). For example, if your code was 15, the system would give one long flash followed by a brief pause, followed by 5 short flashes. If 15 is the ONLY code reported from the ECU, it will repeat this code indefinitely while in test enable mode. If there are multiple codes, the codes will be reported in ascending numeric order, separated by long pauses, and then repeated as a group. For example, if you had code 02 and 15 you'd get 2 short pulses, a pause, one long pulse, brief pause, 5 short pulses, a pause, and then back to the beginning (2 short pulses).

Once you're done checking your codes, this is the part where you get to spend money. Keep in mind that just because the ECU reports a code doesn't mean that sensor needs to be replaced. For example, if you get an O2 sensor lean condition, your sensor could be perfectly fine but you could be sucking in unmetered air through a vac leak, causing the engine to think it's sucking in less air than it actually is. Likewise, your fuel pressure could be low, causing the ECU to think it's injecting more fuel than it actually is. Don't be a slave to your reported codes and blindly replace sensors without first taking a holistic look at the nature of the problem.

  • 02 - no crankshaft position sensor signal
    03 - no cylinder ID sensor signal
    08 - vane airflow meter signal
    09 - electronic coolant temperature sensor
    10 - vane air temperature sensor
    12 - throttle position sensor
    14 - barometric pressure sensor
    15 - exhaust gas oxygen sensor voltage stays below 0.55V (lean)
    17 - exhaust gas oxygen sensor voltage does not change (rich)
    25 - fuel pressure regulator solenoid
    26 - canister purge control solenoid
    34 - idle speed control solenoid
    41 - high speed inlet air control solenoid

edit: typo
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