P1780 and an A343

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Darwood

Darwood

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Oct 8, 2003
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So this last weekend I got a check engine light. I pulled the code and it came out to be a P1780 which is a "Park Neutral Position Switch Malfunction". I cleared the code and it came back after driving a few hours. I cleared it agian and it hasn't come back yet.

I've also noticed that when I put the transmission into 2, the transmission will not downshift into 2nd immediately. It will stay in 3rd or 4th and then abruptly downshift, only to upshift again thus repeating the cycle. It will do this while travelling under a speed that 2nd should be able to downshift into.

My guess is that the 2 problems are related since it appears that the park/neutral position switch tells the ECU what position the gear selector is in.

Now I haven't noticed the gear lights on the dash changing when the transmission does the 3rd gear in 2 thing. Does anyone know what illuminates these lights? I assume it's a signal from the ECU, and that if the park/neutral position switch were telling the ECU that the selector was going between D and 2 that the lights would indicate this.

I haven't had a chance to go throught the diagnostic procedures yet. When I do I'll post what I get.

Does anyone here have some insight into this that they could add to the FSM procedure?
 
in the 96 EWD the cluster lights apear to be controlled directly from the "A/T indicator switch" with the ECu also getting info L, 2, and R info from the At indicator switch, the ECU gets no data from the AT indictor switch about park Drive or neutral

the park neutral switch tells the ECU and starter realy that it is in park/neutral (same signal)

the park neutral switch appears to be a sperate unit electrically although i would not be suprised if they are in the same housing


1. GEAR SHIFT OPERATION
DURING DRIVING, THE ENGINE CONTROL MODULE SELECTS THE SHIFT FOR EACH GEAR WHICH IS MOST APPROPRIATE TO THE
DRIVING CONDITIONS, BASED ON INPUT SIGNALS FROM THE ENGINE COOLANT TEMP. SENSOR TO TERMINAL THW OF THE
ENGINE CONTROL MODULE, AND ALSO THE INPUT SIGNALS TO TERMINAL SP2+ OF THE ENGINE CONTROL MODULE FROM THE
VEHICLE SPEED SENSOR DEVOTED TO THE ELECTRONICALLY CONTROLLED TRANSMISSION. THE CURRENT IS THEN OUTPUT TO
THE ELECTRONICALLY CONTROLLED TRANSMISSION SOLENOIDS. WHEN SHIFTING TO THE 1ST SPEED, THE CURRENT FLOWS
FROM TERMINAL S1 OF THE ENGINE CONTROL MODULE TO TERMINAL 1 OF THE ELECTRONICALLY CONTROLLED TRANSMISSION
SOLENOID " GROUND, AND CONTINUITY TO THE NO. 1 SOLENOID CAUSES THE SHIFT. FOR THE 2ND SPEED, THE CURRENT
FLOWS FROM TERMINAL S1 OF THE ENGINE CONTROL MODULE TO TERMINAL 1 OF THE ELECTRONICALLY CONTROLLED
TRANSMISSION SOLENOID " GROUND AND FROM TERMINAL S2 OF THE ENGINE CONTROL MODULE TO TERMINAL 2 OF THE
ELECTRONICALLY CONTROLLED TRANSMISSION SOLENOID " GROUND, AND CONTINUITY TO NO. 1 AND NO. 2 SOLENOIDS
CAUSES THE SHIFT. FOR THE 3RD SPEED, THERE IS NO CONTINUITY TO NO. 1 SOLENOID, ONLY TO NO. 2, CAUSING THE SHIFT.
SHIFTING INTO THE 4TH SPEED (OVERDRIVE) TAKES PLACE WHEN THERE IS NO CONTINUITY TO EITHER NO. 1 OR NO. 2
SOLENOID.
Click to expand...
 
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