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chengny · 02-19-2015, 07:22 AM

Without knowing the model year and series of the truck you are asking about, it's hard to go into detail. But generally there are 5 permissives that must be met before the ECM will engage the TCC. The permissives are:

1. Road speed - above 30 mph
2. Engine coolant - above 150 F
3. No undue acceleration/deceleration (as per the TPS)
4. Brakes not applied
5. Transmission in either 3rd or 4th gear

A good place to start might be to verify that the TCC is even functional at all. That's an easy test. Just run a temporary 12 VDC power supply (switched and operable from inside the cab) into the wire that runs down to the transmission.

You can then manually energize the TCC whenever you want and see if it locks up.

02-19-2015, 07:22 AM	#2
chengny Registered User Join Date: May 2007 Location: New Hampshire Posts: 349	Re: Don't think I am getting lockup. Without knowing the model year and series of the truck you are asking about, it's hard to go into detail. But generally there are 5 permissives that must be met before the ECM will engage the TCC. The permissives are: 1. Road speed - above 30 mph 2. Engine coolant - above 150 F 3. No undue acceleration/deceleration (as per the TPS) 4. Brakes not applied 5. Transmission in either 3rd or 4th gear A good place to start might be to verify that the TCC is even functional at all. That's an easy test. Just run a temporary 12 VDC power supply (switched and operable from inside the cab) into the wire that runs down to the transmission. You can then manually energize the TCC whenever you want and see if it locks up.