Shift Pointers
- Subject: Code P0770
- Unit: Toyota U341E/F
- Vehicle Applications: Toyota Matrix, Pontiac Vibe
- Essential Reading: Rebuilder, Diagnostician
- Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor
Diagnosing Code P0770
In the Import section of ATSG’s “Shifting Great in 2008” training seminar, one subject that was handled in the Toyota U341E/F segment of the seminar was the elusive code P0770. What makes this code so elusive is that it points to a fault for shift solenoid E. The technician tries to determine which is shift solenoid E and cannot. Nor can the technician determine whether the code indicates an electrical problem or a mechanical one.
This still seems to be a problem, as evidenced by the calls that continue to trickle in on our technical hotline about this dilemma. Code P0770 is a mechanically generated code for the lockup solenoid, which Toyota calls the SL solenoid. The code basically represents anything that can cause the converter clutch to slip. If it were an electrical code indicating a problem with the wiring from the computer down to the solenoid, or the solenoid itself, code P0773 would be set.
Figure 1 shows the location of the SL solenoid. Some repair manuals, including the factory manual, show a lockup control valve in the location illustrated in Figure 2. Of all E and F valve bodies that were inspected, not one had this valve, so this bore being empty does not mean you have found your P0770 problem.
To diagnose the P0770, you should start by checking two valves in the valve body and the SL solenoid. Figure 3 shows the location of the lockup-relay and solenoid-relay valves. Check the bores for wear and to see whether those valves stroke correctly and easily.
Figure 4 illustrates the operation of the lockup system when the converter clutch is off.
Figure 5 illustrates the operation of the lockup system when the converter clutch is on.
Figure 6 explains how to check the SL solenoid with compressed air. Also be sure to check the exhaust circuit of the solenoid when the solenoid is off as explained in Figure 4. If all this checks out, the input-shaft rings, pump and converter will need to be inspected.
