A/T - AX4S Harsh 1-2 Shift Diagnostics

Article No.
97-11-10

05/27/97

TRANSAXLE - AX4S - HARSH 1-2 SHIFT

FORD:
1996-97 TAURUS

LINCOLN-MERCURY:
1996-97 SABLE

LIGHT TRUCK:
1996-98 WINDSTAR

ISSUE:
A harsh 1-2 upshift may be experienced on some vehicles built with the AX4S transaxle. This may be due to high Electronic Pressure Control (EPC) pressure in the transaxle and/or the main control valves sticking in the valve body.

ACTION:
Refer to the following text for diagnostic information.

Perform a self-test of the Electronic Engine Control (EEC) system and follow pinpoint tests for any Diagnostic Trouble Codes (DTCs) displayed. Use the New Generation Star (NGS) Tester to monitor commanded EPC pressure.

EPO pressure at idle in O/D should be 10-20 psi. If EPC pressure is commanded high at idle in OlD without a DTC, use the NGS Tester to monitor Powertrain Control Module (PCM) inputs to locate the concern.

Four (4) sensor inputs that can cause this concern and may not set a DTC are:

^ Vehicle Speed Sensor (VSS)

^ Throttle Position Sensor (TP)

^ Transmission Range Sensor (TR)

^ Turbine Shaft Speed Sensor (TSS)





Install a pressure gauge in the EPC port at the transaxle (Figure 1) and compare actual EPC pressure from gauge to commanded EPC pressure on the NGS Tester. If actual EPC pressure is higher than the EPC pressure commanded by the PCM, the EPC solenoid is mechanically stuck or the pressure failsafe valve is stuck in the valve body. If EPC pressure is correct, remove and inspect valve body for sticking valves, a metal chip and/or contamination that may cause a valve to stick.





Stuck valves that have been found to cause the harsh 1-2 upshift are: the 1-2 shift valve, the intermediate clutch shuttle valve, the capacity modulator valve, the accumulator regulator valve, or the pressure failsafe valve (Figure 2).

OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: INFORMATION ONLY
OASIS CODES: 501000, 503000, 504000