M: Speed Control, PCM, Aerostar EIC, or Electronic Transmission Inoperative or Erratic

NOTE: Follow this procedure only after being referred here by the Speed Control, EEC, AEROSTAR EIC, or electronic transmission shop manual diagnostics.



M1 CHECK REAR ANTI-LOCK LAMP ILLUMINATION


^ Key ON.


^ Does anti-lock lamp on dash go out after self-test?


Yes

GO to M2.


No

REFER to Antilock Brakes/Traction Control Systems Antilock Brakes / Traction Control Systems



M2 CHECK SPEEDOMETER SPEED OUTPUT SIGNAL.



CAUTION: Before checking the continuity of any circuit, make sure there is no voltage present in the circuit prior to switching the test equipment to the resistance function to avoid damage to equipment. Refer to the test equipment user's manual for additional information.


^ Using Rotunda Digital Volt-Ohmmeter 014-00407 or equivalent check for shorts in the wiring between Pin 7 (speed out) and battery/ignition or ground. Is circuit shorted?


^ Use an ohmmeter to check for opens in the wiring between Pin 7 (speed out) and the affected module. Verify that terminals in PSOM wiring connector are completely seated in the connector.

Is the circuit open?


^ Connect an AC voltmeter to Pin 7 (speed out) and Pin 2 (module ground).

Does the voltage increase smoothly and continuously from 0 to approximately 4.5 volts as vehicle speed increases from 0 to approximately 30 mph?


OR


^ If available a frequency counter may be connected to Pin 7 (speed out) and Pin 2 (module ground).

Does the displayed frequency of the signal increase smoothly and continuously from 0 to approximately 67 hz at approximately 35 mph?


OR


^ If neither a voltmeter nor frequency counter is available vehicle speed control may be used as a good indicator. If it works normally above 30 mph this means that the speedometer module is at least receiving a speed input signal and the wiring and sensor can be assumed to be good.

Does speed control work?


Yes

SERVICE wiring between speedometer and affected module as required. VERIFY proper operation.

No

GO to M3.



M3 CHECK SPEED INPUT SIGNAL



CAUTION: Make sure multimeter is in the voltage function and not in the resistance function to avoid damage to multimeter.


^ Connect Rotunda Digital Volt-Ohmmeter 014-00407 or equivalent to Pin 4 (speed/in +) and Pin 5 (speed/in-).

Does the voltage increase smoothly and continuously from 0 to approximately 3.5 volts as vehicle speed increases from 0 to approximately 30 mph?


NOTE: Only the wiring harness end of the connector should be probed.


OR


^ If available a frequency counter may be connected to Pin 4 (speed in + ) and Pins (speed in - ).

Does the displayed frequency of the signal increase smoothly and continuously from 0 to approximately 667 hz at approximately 30 mph?


NOTE: Only the wiring harness end of the connector should be probed.


Yes

REPLACE instrument cluster.


No

SERVICE wiring. CHECK for opens or shorted wiring. If no problems are found, REFER to Antilock Brakes/Traction Control Systems Antilock Brakes / Traction Control Systems