You are right there is no buffer .. and as you say changeing the cluster would have no affect on transmission function !! you could check these out ..or as you say it could be the PCM but without it throwing out codes .. it's hit and miss to locatle the fault ! I would check the TPS first before replacing the PCM
Transmission Fluid Pressure (TFP) Switch (4L60-E & 4L80-E Transmission)
The TFP is actually 5 pressure switches combined into a single unit mounted on transmission valve body. The PCM/VCM supplies battery voltage on 3 separate wires to TFP. As switches are actuated in various combinations during transmission operation, PCM/VCM can detect what gear range transmission is in.
Throttle Position (TP) Sensor
TP sensor is a variable mechanical resistor connected directly to throttle shaft linkage. TP sensor has 3 wires connected to it. One is connected to a 5-volt reference voltage supply from PCM/VCM, another is connected to PCM/VCM ground and third is a signal return which is monitored by PCM/VCM. Voltage signal from TP sensor varies from closed throttle (0.5-1.0 volt) to wide open throttle (4.5-5 volts). PCM/VCM uses this signal to determine control of fuel, idle speed, spark timing and Torque Converter Clutch (TCC). A problem in TP sensor circuit may set a related diagnostic trouble code.
Transmission Fluid Temperature (TFT) Sensor (4L60-E, 4L80-E & 4T60-E Transmission)
TFT sensor is a thermistor (temperature sensitive resistor) mounted to the transmission valve body. The PCM/VCM supplies and monitors a 5-volt signal to TFT sensor. This monitored 5-volt signal is then modified by resistance of TFT sensor. When transmission fluid temperatures are low, TFT sensor resistance is high and PCM/VCM sees a high monitored voltage signal. When transmission fluid temperatures are high, TFT sensor resistance is low and PCM/VCM sees a low monitored voltage.
PCM/VCM uses TFT sensor input to control Torque Converter Clutch (TCC) application and shift quality. Sensor circuit problem should set a related diagnostic trouble code.
Saturday, March 14th, 2009 AT 7:00 AM