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Old 07-19-2012, 11:03 AM   #1
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Default Transmission Swap / PCM Compatibility

The engine in my 1999 LeSabre Custom quit yesterday. I have a 1997 parts LeSabre Limited 3.8 with a 4T60-E. I want to put the engine with transmission in a 1999 LeSabre Custom 3.8 with a 4T65-E because I think that'* on its way out too. From what I gather the PCM and harness need to go with the trans but does anyone foresee problems with installing the 97 PCM in the 99 car? Or should I keep using the same 1999 PCM?
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Old 07-19-2012, 07:02 PM   #2
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Keep the 99 PCM. Compare the electrical connectors on both transmissions. If they are the same, I believe you should be fine.

Also, your taking a 97 engine and putting it into a 99, sensors do sometimes change throughout the 95-2005 years on the 3800. Just take all the 99 sensors off and swap them over. Yes, I have done my homework before.
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Old 07-20-2012, 06:51 PM   #3
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The trans electrical plugs are different between the two cars. The giant plug on the firewall seems to be the same and has the same color wires so the current plan is to plant the '97 PCM in the '99. Here'* hoping it plays nicely with the newer car.
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Old 07-20-2012, 09:09 PM   #4
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The 99PCM will be fine. But, if your going to swap the trans, your going to have to swap the harness also because of the different connector.
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Old 07-20-2012, 11:57 PM   #5
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Engine / trans in both cars are almost ready to be pulled. Only one set of axles and two power steering pumps left I believe. Hopefully the '97 set will wake up for us in the '99 sometime tomorrow. Since the the 4t65-e replaced the 4t60-e starting in '98 models we are concerned that the '99 PCM isn't programmed to run the 4t60-e although I'm not sure it won't. Are there benefits to using the '99 PCM or detriments to using the '97? Do you know if the PCM plays a role in the operation of the blower and radio button style vent selection in these models? You probably know more about these cars than I do and I appreciate your input.
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Old 07-21-2012, 05:35 AM   #6
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As far as the 99 PCM controlling the 65E, I'm not sure. But, I don't see why not due to them being in the same year range.

I believe you would have problems with the 97 PCM in a 99 body. Things like your instrument cluster could be different, your fuel sending unit, HVAC, etc.

When your vehicle is inspected every year, do they hook it up to a computer to check emissions? Not the exhaust, but the computer? If it sees a different year/VIN, it could fail.
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