Overdrive band (A) and TCC Lockup | Ford Explorer Forums - Serious Explorations

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Overdrive band (A) and TCC Lockup


Well-Known Member
November 14, 2011
Reaction score
City, State
Amsterdam, Netherlands
Year, Model & Trim Level
1991 Ford Explorer XLT
Hi All!

I've been trying to diagnose what's going on inside my A4LD, but I'm running into some things. Right now, I'm doing about 3k RPM at 65MPH, and 3.2k RPM at 75 MPH. (3.55 rear diff, standard 235/75/15 tires)

I am certain TCC does not lock up, due to the fact that if i tap the break (also if I tap it a bit more aggressive), the RPMs do not bother to change the least.
Going by page 17 of the ATSG, for EEC providing TCC lockup signals; When using cruise control, the CC will disengage the second I tap the brake, leading me to believe the brake switch is just fine. Engine coolant shows in the normal range on the dash, so that is also fine. I know there are no quick tip-ins or tip-outs, but there could still be some EEC failure, right?

So I've read in other topics, that if the EEC serves as a ground switch for the purple/yellow wire, connected to the TCC solenoid. If it reads 0 volts, the EEC prevents lockup, if it reads 12 volts, the EEC says lockup whenever you're ready. Now, to measure this, can I connect a volt meter's plus wire to the P/Y wire, and the black one to the ground wire? or would I have to connect both the plus and ground wires of the volt meter to the purple/yellow wire? I'm somewhat unclear about this and would love some insights :) Going from the diagram on P18, I should connect two wires to the P/Y wire and measure voltage change...

I am not certain about the workings of my 4th gear. If I go at highway speeds, and shift from OD to D, you can feel the shift inside the transmission, and RPMs will increase, as you would expect. However, when looking at the ATSG manual, I found the following table:

So it could be that I only feel the unlocking of overdrive band B when going from OD to D, assuming it's in third gear, and it never reaches the stadium where only band A is engaged?

How would I find out if band A ever gets engaged? I've read you can check the three wires on top of the transmission for 3/4 shift signals from the PCM, but is that a general "OK, overdrive, you can engage now" signal, regardless of 1st,2nd or 3rd gear, or is that the, "OK, 3rd gear sit back, overdrive band A's got this" ? In the latter case, the engagement can be checked in the same way the TCC is checked. but if the first case is true, then how would you know if there ever is a shift from the OD/3 to OD(4) ?