QuestionQUESTION: I hate to bother you again but I still have not found the source of the high voltage on my TPS but I needed to ask will a short affect my transmission because it is now acting strange sometimes when I let off the throttle to begin slowing down it will downshift sometimes at 50 mph or so and shift so hard it will pull me out of the road almost.
ANSWER: Hi Steve,
Yes, the throttle position sensor signal is indeed monitored by the transmission control module to alter the gear of the transmission so if there were a wrong TPS signal suddenly sent to the tcm it could very well cause a downshift such as you experience. You didn't tell me what is the operating voltage at that sensor pin 3 wire, by the way. You said the pcm is putting out 6v but from what you told me in the beginning the voltage appeared to be much higher. You must have an intermittent short to that wire arrising somewhere in the harness.
I really appreciated your rating and giving me a nomination for volunteer of the month.
Roland
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QUESTION: When I check the voltage at the TPS connection with the switch on it is 12 volts but when I checked it at the PCM like you told me it was 6 volts. I'm not sure what you mean by sensor pin 3, do you mean the TPS or are you talking about on the PCM?
ANSWER: Hi Steve,
I was pointing out that the voltage at pin 3 of the TPS plug is 12 volts when it is supposed to be 5 volts. And when we measured what pin 61 is putting out (absent the pcm plugs but with the pcm powered up by jumpmers, it was indeed putting out something close to 5 volts. So there has to be short between a wire that is carrying 12v and the violet/white wire that is supposed to carrying only 5 volts. There are two wires carrying 12v (on pins 20 white/black, and 46 red/white) and there is also a dark green wire on pin 4 of the pcm that will intermittently show 12v that is related to controlling the alternator field coil). I would suggest that you measure the resistance between pin 61 on the one hand and pins 4, 20 and 46 of the pcm plugs with the tps unplugged and the plugs removed from the pcm. These three readings should be infinite ohms. If they are, then try reading between pin 61 and every other pin of the other 75 pins on the pcm plugs. Somewhere there has got to be short circuit.
Roland
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QUESTION: I'm going to ask one more question and I will leave you alone you have given me a lot of information and I believe you are right I just can't find where the short is. But is it possible that the PCM is bad causing this? I have traced those wires and cannot find any bad wires unless I have missed something. Thank you so much for your help.
Answer I cannot understand how pin 61 of the pcm is showing 6 volts unplugged but then when you actually put it together the voltage is 12 volts, unless there is a short in the wiring to the wire on pin 61. That wire not only goes to the TPS but also to the map and the ac pressure sensor so the short could also be in those branches of the violet/white wire. I can't see how the pcm output voltage would jump to 12 by attaching its wire to the tps/map or pressure sensor because 12v is not used on any of the wires to those sensors. It has to be a short circuit in my mind. The tps signal wire also goes go to the tcm but I can't see how that could boost the voltage on the violet/white to 12v regardless of the position of the throttle.
Roland
