Having problems with your 1998 Ford Expedition ?

1999 ford expedition - transmission slip?

\015 Noticed that the tranny seems to slip but it may just be that it is not shifting into higher gears. High RPM's but low ground speed.Also noticed that Overdrive light is blinking.Seems to run fine with cold engine/ tranny, but gets worse as it warms up.\015 Posted / edited by AnonymousUser on : 25-06-2018

Answers :

The flashing O/D light usually means you have a bad speed sensor that sends speed info to the engine & trans computer.
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\015\012Vehicle Speed Sensor \015\012The vehicle speed sensor (VSS) (Figure 42) is a variable reluctance or Hall-effect sensor that generates a waveform with a frequency that is proportional to the speed of the vehicle. If the vehicle is moving at a relatively low velocity, the sensor produces a signal with a low frequency. As the vehicle velocity increases, the sensor generates a signal with a higher frequency. The PCM uses the frequency signal generated by the VSS (and other inputs) to control such parameters as fuel injection, ignition control, transmission/transaxle shift scheduling and torque converter clutch scheduling.
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\015\012Vehicle Speed Sensor \015\012The vehicle speed sensor (VSS) (Figure 42) is a variable reluctance or Hall-effect sensor that generates a waveform with a frequency that is proportional to the speed of the vehicle. If the vehicle is moving at a relatively low velocity, the sensor produces a signal with a low frequency. As the vehicle velocity increases, the sensor generates a signal with a higher frequency. The PCM uses the frequency signal generated by the VSS (and other inputs) to control such parameters as fuel injection, ignition control, transmission/transaxle shift scheduling and torque converter clutch scheduling.
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\015\012Some trans use an OSS, Output Shaft Sensor instead of a VSS. Depends on which trans you have, 4R100 or 4R70W
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\015\012Transmission Control Switch (TCS) and Transmission Control Indicator Lamp (TCIL)
\015\012The transmission control switch (TCS) is a momentary contact switch. When the switch is pressed, a signal is sent to the powertrain control module (PCM) to allow automatic shifts from first through fourth gears or first through third gears only. The PCM energizes the transmission control indicator lamp (TCIL) when the switch is off.
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\015\012 The TCIL indicates overdrive cancel mode activated (lamp on) and electronic pressure control (EPC) circuit shorted (lamp flashing) or monitored sensor failure.
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\015\012Output Shaft Speed (OSS) Sensor
\015\012The output shaft speed (OSS) sensor is a magnetic pickup, located at the output shaft ring gear, that sends a signal to the powertrain control module (PCM) to indicate transmission output shaft speed. The OSS is used for torque converter clutch control, shift scheduling and to determine electronic pressure control.
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Repair Help & Product Troubleshooting for 1998 Ford Expedition

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