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Throttle Position Sensor
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The throttle position sensor, shift lever, and throttle valve cable are critical to proper operation of the transmission. If one or more of these are out of adjustment or if the TPS is noisy, shifting will be erratic. Before performing any adjustments, check the transmission fluid level and sniff the fluid. Do not make any adjustments until the fluid level is correct, and burned fluid has been replaced.
The service manual says to adjust for 0.8-1.2V at idle. On many trucks, this voltage is too low, resulting in TCC chatter at moderate throttle loads. The TPS is not officially adjustable but the mounting holes are slotted and the body can be rotated slightly. Adjustment is relatively easy, and requires only a digital voltmeter and a few hand tools. A little adjustment goes a long way...
TPS wire color code:
Testing and adjusting the TPS:
1. With the key "OFF", unplug the connector from the TPS.
2. Turn the key "on" and insert DVM probes into the connector to reach the connector pins. Short pieces of wire or paper clips can be used to extend the DVM probes for reaching into the connectors.
3. Read from the purple wire to the black wire (these should be the outside pins). Power should be 5V with the key "on".
4. Turn the key "off" and plug the connector back onto the TPS
5. Insert the leads from the digital volt meter into the back of the TPS connector. The DVM negative probe goes into the back of the connector cavity with the black wire. The positive DVM probe goes into the back of the connector cavity with the orange signal wire.
NOTE: Push the probes into the rear of the connector until the probe tips reach the metal connector pins.
6. Loosen the TPS mounting screws
7. With the engine off and key on: Adjust the TPS position for 1.2 to 1.5V on the signal wire with the throttle at the idle position - more voltage makes more TC clutch pressure, too much will set a fault code. Often, adjusting for 1.4 to 1.5V at idle will cure TC clutch chatter under light load conditions. NOTE: The factory setting is 1.2V max, so proceed carefully.
8. Tighten the TPS screws, slowly open the throttle to the WOT position and then return return to idle. Watch for voltage jumps - the voltage should change smoothly from the idle value to at least 3.5V at WOT (5 volts is all you should be able to get). If the sensor voltage jumps or drops unexpectedly - replace the sensor or try the filter modification below.
Posted to a TPS thread on the TDRoundtable by Bill Kondolay (Bill
is one the true transmission experts out there):
Before anyone follows advice on how to adjust the TPS
keep in mind that every action has a reaction. You can adjust the TPS
voltage to pretty much what ever you want without following Chryslers
procedures. Before starting, always record your original idle voltage;
you must have a baseline to start from.
TPS Filter Construction - Bring a dead TPS back to life
Steve Clayton Gemcuttr1@cs.com sent this simple technique for filtering the output of a noisy TPS.
I did some experimenting and found that an electrolytic capacitor (440 microFarads, 35 Vdc) with the negative side connected to the SIG RETURN wire and the positive side hooked to the TPS SIG wire gave me absolutely *troublefree* operation! Even though my TPS is basically trashed, the capacitor filters out almost all of the electrical noise, and my auto tranny once again shifts like factory-new!
I dug into the wire bundle coming out of the PCM and soldered the capacitor as close to the plug as I could manage - thinking some "TPS problems" may actually be wiring/connector problems in disguise.
Results with other values were:
BTW, I might add that since I added the capacitor, my cruise control hasn't dropped out even once in 15K miles - usually a twice-per-week occurence (I drive 1500 miles a week). What I believe is that the dropout problem is caused by an electrical noise spike from the TPS - which is *exactly* what the capacitor filters out.
Please consider this tip a free gift for oilburner fans! The capacitor costs just 40 cents, and I hope it will save TDR members and others lots of money! After all, you can by a lot of #2 diesel for $200! :-)
Last Update: November 29, 2001