Transmission Fluid Pressure Manual Valve Position Switch
The Transmission Fluid Pressure (TFP) manual valve position switch assembly consists of two normally open pressure switches. The assembly is attached to the lower control valve body. The PCM supplies ignition voltage on the two range signal circuits, signal circuit "A" and signal circuit "C". By grounding one of the switches with fluid pressure from the manual valve, the PCM detects a garage shift from Park/Neutral to Reverse or Park/Neutral to Drive. See TFP MANUAL VALVE POSITION SWITCH LOGIC table. This information is used by the PCM to adjust line pressure during garage shifts.
| Range Signal | Signal A | Signal C |
|---|---|---|
| Park/Neutral | HI | HI |
| Reverse | LOW | HI |
| Drive | HI | LOW |
| Invalid | LOW | LOW |
| (1) HI = ignition voltage; LOW = zero volts. | ||
| (1) | HI = ignition voltage; LOW = zero volts. |
TFP MANUAL VALVE POSITION SWITCH LOGIC (1)
Transmission Fluid Temperature Sensor
The Transmission Fluid Temperature (TFT) sensor controls TCC and line pressure. The TFT sensor attaches to the upper control valve assembly. The TFT signals the PCM regarding transmission fluid temperature. The sensor is a negative temperature coefficient thermistor which receives a 5-volt signal from the PCM.
When the temperature is cold, the sensor resistance is high; therefore, the PCM sees a high signal voltage. As the fluid warms, the sensor resistance decreases, and the voltage drop across the sensor becomes lower.
The TFT sensor may be tested with an ohmmeter across terminals "L" and "M" of the transaxle in-line 20-way connector. Nominal ohm readings at specified temperatures are given in voltage levels at the PCM. (Схема №53)
The temperature sensor mode operates in the following two ways
- Hot Mode Enable Above 266°F (130°C) and TCC on in 3rd gear at 30 MPH with 0-10 degree throttle angle; and 4th gear at 39 MPH with 0-10 degree throttle angle. This reduces transmission temperature by decreasing the amount of heat generated in the torque converter. It also provides maximum cooling by routing transmission fluid directly to the transmission cooler in the engine radiator.
- Super Hot Mode Disable On 275 HP RPO LD8 Engine Above 284°F (140°C) and TCC off with 4th gear inhibited. Super hot is a condition where a hot engine adds heat to the transaxle through the transmission cooler. By inhibiting TCC and 4th gear operation, the engine works under less load. This reduces the heat added to the transmission fluid by the transmission cooler. As both the engine and the transaxle cool off, TCC and 4th gear are permitted again.
A PCM internal shunt circuit comes into play as the temperature increases beyond 122°F (50°C). As the temperature decreases, the internal shunt comes out at 104°F (40°C). There is a 18°F (10°C) overlap.
Note. Manufacturer does not provide on-vehicle removal and installation procedure for this component. See appropriate OVERHAUL article.