dstrick32

Just got though changing out my engine,(3.0) adding Downey headers and doing other mechanial repairs to the trans and transfer A340H, nothing internal. Both the speedometer and the 4X4 on light in the dash stopped working. Everything else works fine and 4WD is engaging. Trying to figure out what these two have in common that might be causing this problem. The light bulb is good. OD, ECT and AT Temp lights work!! Anybody got an idea?? These factory electrical diagrams leave alot to be desired!! Any suggestions will be appreciated!!

wrenchmonster

Sounds like a speed sensor problem. Codes?

-Wrench

dragon564

I think you might have missed plugging in some of the wiring harness back on the tranny. There are several that have to be plugged back in. the selection of P-R-N-D-2-L and 2H-4H-4L are a mechanical function and not electronic. OD is electronic but the ins pnl light is controled in part the button on the shifter if the button is off the OD OFF is on if the button is on the the OD OFF is not lit, This is true when the tranny is out of the truck. If the electronics are not plugged in OD MIGHT NOT work the truck MIGHT not shift into OD the ECU will detect that and casue the OD OFF light to flash this detection will only occur when the truck should shift into OD, so you could drive around the block at 30 and never know that OD is not working properly. the MIGHT is there becasue some of the older A340H's can shift into OD with out the electronics working.

dstrick32

I check them all and they were pluged in but will check again since I did move some wires around to clear the headers and exhaust!! Thanks for the get back!!

Haven't checked for codes but will do so since the CEL is on but haven't got the o2 hooked up yet and figure that was the reason for light!! Thanks!!

dragon564

With the headers added...did the wire bundle get to close to the exh and brun????

dstrick32

No I got them all cleared before firing it up!! Thanks!!

dstrick32

Wrenchmonster and others involved reading codes 14, 21 & 42. The 21 is explainable since the o2 isn't hooked up yet. The 14 IGF signal from igniter is not input to ECM for 6 consecutive ignitions & 42 SPD signal is not input to the ECM for at least 8 seconds during high load driving with engine speed between 2,750 rpm and 4,000 rpm are the ones that I can't explain!! Help needed can not make heads or tails from this FSM. Need something a shadetree mechanic can understand. As you can tell these computers aren't my cup of tea!! Open for suggestions that I can understand. All connection are in place as best I can see. Will get under there and hand check each one for good clean connection!! Thank you!!

dragon564

Connect the o2 and clear the 21 code, I dont think it will help out at all with the 14 code but it , will at least be one less code to deal with....the 42 SPD code is telling you the ECU is not getting the SPEED input from the tranny which you already know as the speedo is not working, but it is getting input from the distributor telling how fast the motor is turning, and it has the signal that tells it the truck is not in P or N
hope that helps.....

dstrick32

Found the problem on codes 14 & 42. Terminal SP1 at ECM wasn't grounging. Does anybody know where the transfer on indicator switch is located on the 94, 3.0, 4X4, Auto, A340H trans?
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dstrick32

Rid of all codes, speedometer working and still trying to find out what controls the 4WD indicator in dash. Bulb good, 4WD working and no ADD on vehicle. A340H auto. Has anyone got any idea if there is a switch that controls the indicator and where it might be??