Oil Pressure Switch - Information
Number 83-I-168 Section 7 Date 12/83Subject: OIL PRESSURE SWITCH INFORMATION - THM 700-R4 TRANSMISSION
Figure 1 - Control Valve Assembly:
The THM 700-R4 transmission has four oil pressure switch locations in the control valve assembly (see Figure 1)..
Depending on vehicle type, various oil pressure switches will be used in these locations. When no switch is used, a 1/8 inch NPT pipe plug (Part Number 44612) is installed in place of the switch.
On vehicles built without an electronic control module (ECM) these switches control the torque converter clutch operation and exhaust gas recirculation (E.G.R.) bleed system. On ECM equipped vehicles these switches help supply information to the ECM about the transmission operation. The ECM also controls various functions including fuel mixture, engine timing, engine idle, and torque converter clutch (T.C.C.) operation. If switches are wrong, mislocated, or malfunction, various electrical and mechanical problems may result, i.e., blown fuses, instrument panel lights remaining on without apparent reason, or improper engine operation.
Figure 2 - Switch Description:
General Switch Description
Oil pressure switches are activated by hydraulic pressure from the control valve assembly. Depending on design, a switch may function as the ground for an electrical circuit or as a simple connecting switch. All switches are designed to be either normally open (N.O.) or normally closed (N.C.).
N.O. - Means the switch will not allow electric current to flow until the switch is activated by hydraulic pressure.
N.C. - Means the switch will allow electric current to flow until the switch is activated by hydraulic pressure.
Also, the switches may be designed with either one or two terminals (see Figure 2). Single terminal switches are used to provide an electrical ground while two terminal switches act as connecting switches.
Figure 3 - 3rd Clutch Switch:
1. "Torque Converter Signal" switch (Part Number 8642473).
This is a single terminal normally open switch. The function of this switch is to make an electrical ground when the converter clutch is applied and break the ground when the clutch is released. For all 1982 and 1983 non-ECM vehicles with T.C.C. signal, this switch is wired in series with the 3rd clutch switch (see Figure 3).
2. 3rd Clutch Switch (Part Number 8643710)
This is a two-terminal normally open switch. It is currently wired in series with the T.C.C. Signal Switch and allows current to flow to the T.C.C. Signal Switch only when the transmission is in third gear, although the high altitude option is an exception. The combined function of the 3rd Clutch Switch and T.C.C. Switch is as follows:
A. 12 volts C.D. 0.20 AMP electric current is sent across the E.G.R. solenoid (60). With either switch open, the current cannot flow. This signals the EGR solenoid that the transmission is not in third gear and that the converter clutch is released. When the transmission is in third gear and the converter clutch is applied, the electrical current from the EGR solenoid flows through the 3rd clutch switch and grounds through the T.C.C. signal switch. This signals the EGR solenoid to release emission control (see Figure 3).
Figure 4 - 4-3 Downshift Switch:
3. 4-3 Downshift Switch (Part Number 8642346)
This is a normally closed two terminal switch. The 4-3 downshift switch is sometimes referred to as a pulse switch and performs the function of releasing the converter clutch when a 4-3 downshift is made (see Figure 4). The 4-3 downshift switch is activated by exhaust oil from the 4th clutch. After the 4th clutch oil has exhausted, the switch closes and allows the converter clutch to reapply. This momentary release (pulse) of the converter clutch allows the transmission to make a 4-3 downshift without any objectional shift feel.
Figure 5 - 4th Clutch Switch:
4. 4th Clutch Switch
One of three different switches may be installed in this location depending on vehicle usage.
A. 4th Clutch Switch (Part Number 8643710)
This switch is a normally open two terminal switch. The function of this switch is to keep the converter clutch applied in 4th gear regardless of engine vacuum (see Figure 5).
Figure 6 - 4th Discrete Switch:
B. 4th Discrete Switch (Part Numbers 8634475 or 8842569)
These are normally closed single terminal switches. They are used in vehicles with ECM's. The purpose of either switch is to signal the ECM when the vehicle is in 4th gear (see Figure 6).
Figure 7 - 4th Clutch Switch:
C. 4th Clutch Switch (Part Number 8642473)
This is a normally open single terminal switch. The function of this switch is to keep the converter clutch applied in fourth gear regardless of any other controls (see Figure 7).