GMC Troubleshooting Questions? Ask a Mechanic for Answers
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The codes P1870 here can indicate an internal mechanical fault in the transmission itself with the valve body or another internal mechanical component and is most likely tied into the P0751 code as well.If the valve body has not been tested at all this needs done to see if it needs replaced or if there is another internal mechanical fault in the transmission needing replaced to correct this fault here.
If you have a cam/crank correlation fault code set this may be an issue with a worn gear on the distributor shaft needing replaced as I have seen before.If you can post this code here this will help.
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