Diagnostic Aids

An intermittent may be caused by rubbed through wire insulation. Check for:

Boost control driver circuit shorted to ground.
Intermittent Test

Disconnect PCM Blue connector and install a DVOM to monitor voltage between PCM harness boost control driver circuit terminal and ground. With ignition on, observe voltage while moving related connectors and wiring harness. If failure is induced, voltage reading will change.

Fig 1: Code P1257 Schematic (3.8L) Transmission Shift Solenoid "B"

Fig 2: Code P1257 Flow Chart (3.8L) Transmission Shift Solenoid "B"

NOTE: Prior To Performing This Chart, Verify Presence Of At Least 15 In. Hg Vacuum To By-Pass Actuator Solenoid With Engine Idling. Also Verify Lines Are Not Plugged. Repair Any Vacuum Supply Problems.

Fig 3: Code P1257 Flow Chart