LINCOLN LS 5R55S HARSH ENGAGEMENTS AND/OR HARSH SHIFTS
Before or after an overhaul, 2003 and newer Lincoln LS vehicles equipped with the 5R55S transmission may exhibit a complaint of harsh engagements and/or harsh up-shifts (especially the 1-2), with no codes stored in the PCM. This complaint will typically come into ATSG's technical hot line as the reason the vehicle came to the shop in the first place. During overhaul the solenoid assembly was replaced and at times a complete valve body yet the problem remained.
The cause may be a PCM that is incorrectly controlling solenoids producing high main line pressure. This style transmission has three pressure control solenoids with which to control shift feel. Pressure Control Solenoids A, B and C otherwise referred to as PCS A, PCS B and PCS C.
Pump pressure for the transmission is regulated by a pressure regulator valve in the valve body. The PCM operates pressure control solenoids A and B individually to influence this valve raising and lowering main line pressure according to temperature, engine load and shift programming. (Refer to Figures 1 and 2 for a description of the Pressure Regulator Valve and how PCA and PCB act on the Boost Valve to influence line pressure).
Since these two solenoids work together to control main line pressure, only one pressure tap is needed with which to observe the pressure via a gauge or transducer.
To verify that the harsh engagements and shifts are the result of high line pressure, attach a gauge or transducer to the pressure port identified in Figure 3. Idle pressure in the Drive position should be approximately 100 psi (Figure 4). If 150 psi is seen this may indicate problems related to PCM control. The chart in Figure 5 is a list of pids for the pressure control solenoids from a lap top scan tool along with information explaining when these solenoids are producing low signal pressure (L) to high signal pressure (H). This can then be compared the solenoids amperage to determine if the problem is related to the computer or not.
The easiest way to do this is to locate pin 1 for PCS B and pin 11 for PCS A at the solenoid body connector (Figure 6). Connect an amp clamp with each solenoid one at a time and monitor the amperage. Approximately 0.75 to 0.98 amps should be observed when the solenoid is supposed to be producing low signal pressure in its respective circuit at idle. The typical reading when there is a PCM problem will be near 0.23 amps.
To verify that the amp readings are not normal, make sure that all connections are clean from the PCM to the Transmission. Check run monitors and Mode 6 data to eliminate any possibility of the computer being in a Failure Mode Affect Management state yet not producing codes. If all is well replace PCM. Note: the PCM will need to be programmed by a dealer when installed.
