1998 GMC Jimmy have 2-Hi and 4-Low but No 4-HI?
#1
10-12-2017, 04:19 PM
1998 GMC Jimmy have 2-Hi and 4-Low but No 4-HI?
Ok I have read a lot of forum info, watched a load of you tube, and nothing has helped.
When I start engine I have no lights on the 4x4 selector switch, I have to put the shift selector in Neutral then I can use the buttons and it shifts into 4-Low Sometimes I get 2 lights lit and sometimes I get no lights but its in 4-Low at this point. At the same point it will not shift into 4-Hi, It shifts fine back into 2WD but no lights on the switch.
This is what I have tried, I have replaced the Encoder with a brand new Encoder from Autozone. I have cleaned the contacts into the TCCM with vinegar/salt as there was some green corrosion after which i coated it with dielectric grease, the contacts with the encoder looked clean.
Is there any way to test a TCCM? I really do not want to just continue replacing parts when there should be a way to test them somehow. Any help would be appreciated.
When I start engine I have no lights on the 4x4 selector switch, I have to put the shift selector in Neutral then I can use the buttons and it shifts into 4-Low Sometimes I get 2 lights lit and sometimes I get no lights but its in 4-Low at this point. At the same point it will not shift into 4-Hi, It shifts fine back into 2WD but no lights on the switch.
This is what I have tried, I have replaced the Encoder with a brand new Encoder from Autozone. I have cleaned the contacts into the TCCM with vinegar/salt as there was some green corrosion after which i coated it with dielectric grease, the contacts with the encoder looked clean.
Is there any way to test a TCCM? I really do not want to just continue replacing parts when there should be a way to test them somehow. Any help would be appreciated.
#2
10-13-2017, 08:20 AM
Ok I have read a lot of forum info, watched a load of you tube, and nothing has helped.
When I start engine I have no lights on the 4x4 selector switch, I have to put the shift selector in Neutral then I can use the buttons and it shifts into 4-Low Sometimes I get 2 lights lit and sometimes I get no lights but its in 4-Low at this point. At the same point it will not shift into 4-Hi, It shifts fine back into 2WD but no lights on the switch.
This is what I have tried, I have replaced the Encoder with a brand new Encoder from Autozone. I have cleaned the contacts into the TCCM with vinegar/salt as there was some green corrosion after which i coated it with dielectric grease, the contacts with the encoder looked clean.
Is there any way to test a TCCM? I really do not want to just continue replacing parts when there should be a way to test them somehow. Any help would be appreciated.
When I start engine I have no lights on the 4x4 selector switch, I have to put the shift selector in Neutral then I can use the buttons and it shifts into 4-Low Sometimes I get 2 lights lit and sometimes I get no lights but its in 4-Low at this point. At the same point it will not shift into 4-Hi, It shifts fine back into 2WD but no lights on the switch.
This is what I have tried, I have replaced the Encoder with a brand new Encoder from Autozone. I have cleaned the contacts into the TCCM with vinegar/salt as there was some green corrosion after which i coated it with dielectric grease, the contacts with the encoder looked clean.
Is there any way to test a TCCM? I really do not want to just continue replacing parts when there should be a way to test them somehow. Any help would be appreciated.
To diagnose a TCCM you need a Tech2 scanner and factory shop manual diagnostic charts - the Chevy dealerships have them. But the Tech 2 is too expensive for the common person and the $300 Chinese clones are iffy.
The lights in the 4WD Selector switch are driven by the TCCM. If you want to test the actual selector button function it you can check each button of the switch by reading resistance on specific wires with multimeter at the TCCM connector while pressing them. Values you should obtain, as well as complete 4WD wiring diagrams are in tech section of this site. I doubt if there will be a problem with the switch. Auto 4WD is RPO NP8
So if you have replaced the encoder motor and test the switch and all the power feeds are good - then it has to be the TCCM (which I think makes sense if you found any corrosion).
Best wishes for a successful repair.
p.s. Summit Racing will beat any price you find on the Internet and has very good and easy return policy in general. I bought the Cardone TCCM for mine. Here is the one that you need for 2001 NP8 (auto 4WD). You can buy almost anything that you want from Summit if you know the manufacturer's part number and enter it into their search engine - they have it drop shipped to you. Also enter the part number into Google and search the Internet for even better deals - then call Summit and they will beat the price. I buy everything I can from Summit as they ship overnight (ground shipping) from Ohio to Indiana for stuff they have in stock. If you need to return a part for any reason, just tear off the return part of your invoice, fill it out, and use their shipping arrangements (see return invoice). You will need to pay for return shipping on any return and they will credit your card back for the balance. Note this part has a core charge of $100. IIRC I had to call Summit to get them to pay for shipping the core back - but they agreed (argument is that the part is pricey enough for 'free shipping" which would include shipping of any cores back to them.
https://www.summitracing.com/int/sea...illocation=int
Last edited by LesMyer; 10-13-2017 at 08:56 AM.
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