P0638 Mercedes-Benz Auto Trouble Code

P0638 Mercedes-Benz Auto Trouble Code on vehicles with electronically controlled automatic transmissions, the 3-4 shift solenoid is responsible for actuating the hydraulic circuits to activate clutches or bands that change gears inside the automatic transmission.

The crank but won't start condition, along with the trouble codes may make you think you've got a PATS anti-theft system problem. However, Ford reports that these codes are all related to software bugs. The only way around the problem is to reprogram the PCM with the latest software.

P0638 Mercedes-Benz Possible Solution:

Power Steering Pressure (PSP) Switch Signal Malfunction The PCM counts the number of times vehicle speed transitions from 0 to a calibratable speed. After a calibratable number of speed transitions the PCM expects that the PSP input should have changed. This DTC is set if the transition is not detected. Vehicle towed with engine running Power steering hydraulic concern was repaired but DTC was not erased PSP switch/shorting bar damaged SIG RTN circuit open PSP circuit open or shorted to SIGRTN PCM damaged Check, if possible, if vehicle was towed or power steering service was performed. Observe PSP V PID while checking wires for intermittents.

P0638 Mercedes-Benz Description For All Models :

P0638 Mercedes-Benz Trouble Repair :

The sensors receive a 5 volt reference signal from the PCM. As pressure readings change, the sensor varies the voltage and the computer reads that to determine input. In the case of a broken wire, the sensor never sees the voltage and the computer assumes a major fault. So if you get this P0638 Mercedes-Benz code, first check to make sure you're getting a good 5 volt reference signal at the sensor.

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