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CODE PO502 & PO503

11-11-2004, 01:30 PM
I'm getting a code of PO502 and one of PO503. The car will out of the blue just feel like it went into neutral when your going down the highway. The speedometer will jump all over the place when this happens. Any ideas??? Thanks for you help!

11-11-2004, 02:26 PM
those are codes dealing with your speed sensors. the speed sensor codes go from PO500 - PO503. That is why your speedometer jumps. Probably need to replace them, but check for bad connections first.

11-11-2004, 02:37 PM
Will that have anything to do with the erratic shifting? The speedometer only acts up when the tranny seem like it goes into neutral.

11-11-2004, 03:24 PM
Yes that is why the transmission is shifting funny. The trans computer relies on the speed of the vehicle and RPM's to determine shift points. If the speed sensor is not working the trans does not know when to shift. On the Aurora there are actually 3 (I think) speed sensors. One each for the input and output shaft speed and I think there is another, maybe not.

The codes are
P0502 Vehicle Speed Sensor Circuit Low Input
P0503 Vehicle Speed Sensor Intermittent

This would probably suggest a short as a short would pull the circuit low. I would have to say that this most likly culprit is wiring as when the speed sensor goes it usually causes an open circuit due to the nature of the sensor, but it could be the sensor it self.

Good luck.

11-11-2004, 03:29 PM
Are they located in the tranny or out side the tranny? Thank you very much for you help. Its the wifes car and she drives the wheels off it.

11-11-2004, 06:20 PM
I believe the VSS is located outside the transmission. I guess there are only two speed sensors. The Turbine Speed Sensor (TSS) and the Vehicle Speed Sensor (VSS). It looks like the VSS is outside of the trans as the labor estimate is only .6 hours. You can also see it here in this diagram.

This is for a 95 but I don't think the 4t80E trans has changed much. The part number for the 95 is 24204319.

The TSS is in the trans and is the really expensive one to replace.

11-18-2004, 09:31 AM
Thanks all! This sensor did the trick it shifts perfect!

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