This procedure will help you diagnose your ill-shifting automatic transmission. This will troubleshoot the electronic portion of the transmission. If your Z has an automatic transmission, you'll have that 'mystery light' on your dash. That's the amber light that has no writing on it, that's the AT light, and the one you need to pay attention to through this procedure. This is according to the Factory Service Manual, AT Section.

AT Light

Shifter Position

A/T Diagnostics:

1. Have the engine at normal operating temperature, in P with the overdrive switch on.
2. Start engine. The AT light should go out after 2 sec.
3. Turn the ignition off.
4. Move selector to drive D by using the Push Release button. If not equipped, use the brake pedal
5. Set overdrive switch to OFF.
6. Wait 2 seconds and turn ignition switch ON.
7. Wait 2 seconds and move selector to 2.
8. Set overdrive switch to ON.
9. Move selector to 1.
10. Set overdrive switch to OFF.
11. Depress accelerator pedal fully and release it.
12. The codes will begin to flash. Theres one long flash that signifies the start of the sequence. Following should be 10 short flashes. Then it repeats.

Error Codes Key:

All 10 flashes the same = No error codes detected.
1st flash longer than others = Revolution sensor is shorted or disconnected.
2nd flash longer than others = Speed sensor circuit is shorted or disconnected.
3rd flash longer than others = Throttle sensor circuit is shorted or disconnected.
4th flash longer than others = Shift solenoid "A" circuit is shorted or disconnected
5th flash longer than others = Shift solenoid "B" circuit is shorted or disconnected
6th flash longer than others = Overrun clutch solenoid circuit is shorted or disconnected
7th flash longer than others = Lock-up solenoid circuit is shorted or disconnected
8th flash longer than others = Fluid temperature sensor is disconnected or A/T control unit power source circuit is damaged.
9th flash longer than others = Engine revolution signal circuit is shorted or disconnected
10th flash longer than others = Line pressure solenoid circuit is shorted or disconnected
All the same with no long start flash = Battery low, been disconnected, or control unit has just been reconnected.

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