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The speedometer reads way to fast. Says your going 55 when your going 30. Used app on my phone front left front right speed sensors match my gps speed. But the rear speed sensor is way off. Replaced it still the same. Reads the same in ecm and in abs module. Calibrated tire size in abs module. About ready to call a pcm. Wondering if I could shim it out and correct the issue?
Shimming out, as you call it, will not correct this issue. The calculated speed depends on the signal frequency and shimming will not change the number of pulses generated at a given speed.
"Supposing" this is a variable reluctance sensor you would only weaken the signal strength by shimming, up to the point where the sensor couldn't pick it up anymore depending on the distance between sensor and tone ring.
On a digital sensor design the signal amplitude would not change proportionally when increasing the distance between sensor tip and tone ring. The signal will be unaffected up to the point where the sensor can't pick it up anymore.
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