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Old 12-18-2009, 03:45 PM
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98 silverado abs/vss issues need help

hi all

my 98 silverado 4wd w/305 in it stopped shifting and the abs light and service engine light came on...and obviously abs doesnt work.

i checked all fuses...didnt find any that i thought were bad.

i read the codes w/an obdII and it gave me code po502 vehicle speed sensor circuit low input. i did a bunch of research and tried to do some tests with a multimeter but didnt know what the heck i was getting.

i went ahead and replaced the PS front wheel sensor at about 112 bucks...no help. i went ahead and replaced the DS front wheel sensor at about 106 bucks...no help.

what the heck do i do???? im a DIY'er and have to solve this myself...but without throwing more wasted money i cant afford.

thanks all for any help!

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Old 12-18-2009, 09:47 PM
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the speed sensor your looking for is near the back of the transfer case.
check the wiring near the sensor for breaks and damaged insulation.
its very common for the wiring to be in poor condition.
if you find a problem with the wiring near the speed sensor, you can get a replacement pig tail to splice in.

unplug the connector and look for signs of trans fluid on the connector.
if the connector or sensor have trans fluid in them, the sensor is leaking and needs to be replaced whether the other checks show the sensor is bad or not.
i normally will replace the pig tail with the sensor if i find a leak.

if everything looks ok so far, pull the sensor out and check it. look for a build up of metal particles on the end. a little bit is normal. clean it off and check for cracks in the plastic and do a resistance check on the sensor.
if you still haven't found a problem, this part can be tricky to do. you may need a mirror. looking thru the hole where the speed sensor goes, check the position of the reluctor inside the transfer case. it should pretty much centered.
in my experience i would say probably 95% of speed sensor related problems are from a wiring problem near the sensor, or the speed sensor itself.


you can do this part first if you want to. i usually don't do it unless i don't find any problems with the speed sensor, the wiring near the sensor, or the reluctor.
using a wiring diagram that has connector views, locate the speed sensor terminals at the PCM. my book shows the connector to be C1, blue in color, terminals C1-29 and C1-30. with the speed sensor plugged in, check the resistance. it should be 1470~2820 ohms.
also, with the speed sensor plugged in check C1-30 for short to ground. it should be greater than 50K ohms.
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Old 12-19-2009, 07:24 AM
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thanks

Quote:
Originally Posted by Soul_Hunter
the speed sensor your looking for is near the back of the transfer case.
check the wiring near the sensor for breaks and damaged insulation.
its very common for the wiring to be in poor condition.
if you find a problem with the wiring near the speed sensor, you can get a replacement pig tail to splice in.

unplug the connector and look for signs of trans fluid on the connector.
if the connector or sensor have trans fluid in them, the sensor is leaking and needs to be replaced whether the other checks show the sensor is bad or not.
i normally will replace the pig tail with the sensor if i find a leak.

if everything looks ok so far, pull the sensor out and check it. look for a build up of metal particles on the end. a little bit is normal. clean it off and check for cracks in the plastic and do a resistance check on the sensor.
if you still haven't found a problem, this part can be tricky to do. you may need a mirror. looking thru the hole where the speed sensor goes, check the position of the reluctor inside the transfer case. it should pretty much centered.
in my experience i would say probably 95% of speed sensor related problems are from a wiring problem near the sensor, or the speed sensor itself.


you can do this part first if you want to. i usually don't do it unless i don't find any problems with the speed sensor, the wiring near the sensor, or the reluctor.
using a wiring diagram that has connector views, locate the speed sensor terminals at the PCM. my book shows the connector to be C1, blue in color, terminals C1-29 and C1-30. with the speed sensor plugged in, check the resistance. it should be 1470~2820 ohms.
also, with the speed sensor plugged in check C1-30 for short to ground. it should be greater than 50K ohms.

thanks for taking the time to give me a thorough answer...much appreciated...i will give a visual recheck of the wiring...i did that twice and didnt think i saw anything but wiring is wacky...i will also check the sensor on the transfer case...thanks again for the tips!
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Old 12-19-2009, 11:28 AM
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problem solved!

i went ahead and changed the tranny mounted VSS and the problems were corrected immediately!

two parts bought that i didnt need and i still saved a bundle!

thanks for helping!
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Old 12-19-2009, 11:56 PM
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no problem
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