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Unread 01-25-2009, 10:29 PM   #1
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1998 ZJ 
Join Date: Jul 2007
Location: Minnesota
Posts: 2,388
PO720 : Output Speed Sensor Circuit Malfunction

Check engine light PO720 came back on after I cleared it yesterday. Output Speed Sensor Malfunction. This came on after I went from a 35 speed gear to a 31 tooth. The spedometer still works though and is more accurate. What should I Do?


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Unread 01-26-2009, 04:19 AM   #2
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Join Date: Sep 2006
Location: USA
Posts: 124
Hi, if you have a 42RE tranny there are 2 speed sensors. one is the vehicle speed sensor which is bolted to the speedometer adapter which mates with the speedometer pinion located on the drivers side of the overdrive housing and the other one is the transmission output speed sensor located just forward of the vehicle speed sensor and it is screwed into the housing. It sounds like you were tinkering with the vehicle speed sensor. the transmission output speed sensor is relatively cheap even at the dealer, less than $25 and can be swapped out easily. check the wires to the connectors and make sure they have not torn out. I had the wires tear out of the transmision speed sensor on mine and it had a delayed and hard shifting but no check engine light. after I repaired the wires the trans shifted like new again. after you replace the output speed sensor if you decide to I read here in this forum somewhere that if you disconnect the battery both wires for 50 or 60 minutes the check engine light will go out but I never had the occasion to try it. One other thing. did you get the indexing correct when you removed the vehicle speed sensor and speedometer adapter from the housing? If you google for 42RE diagram you will get a hit on the 42RE manual and I think on page 21-47 there is an explanation of how to index the speedometer adapter.hope this helps

Last edited by jetdude; 01-26-2009 at 02:30 PM..
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