Hey everyone - I recently acquired a 89 pickup 2.4 22re EFI to A43D auto trans (sure would be dandy if all cars had the trans model on the vin plate). The overdrive btn does cause the dash light to turn on and off - but the overdrive isn't actually engaging when it feels like the conditions are such that it should engage (not 100%, because I lack a tach).
I have a few ideas about how to troubleshoot, but as I'm still getting to know this truck, I figured I'd post here to benefit from those with more experience.

After searching through the forums, here is what I gathered might be some possibilities.
1) sounds like this truck has 2 CTSs - one for the dash gauge, and the other as an interlock to prevent overdrive from engaging cold. The dash sensor seems to work, but perhaps a failure of the second.
2) stuck open/partial open thermostat preventing temp reaching normal operation temp.
3) the OD solenoid itself failed
4) beak in the wiring to the OD solenoid.

Some things I think are not likely:
1) speed or RPM sensor issue seems unlikely as it feels like 1-3 shift normally.
2) failure of the switch on the shifter because the "OD off" functions as expected.

Additions welcomed to either list. I don't have a history with this particular truck, so it's totally possible my feel is off (I would really like to have an actual tach). If anyone has an idea how to approach the issue, I welcome suggestions.

I have next to no experience with overdrives, so a very remedial question: when the overdrive is enabled, will the solenoid only engage when it upshifts from 3rd (so essentially just another gear), or is it always engaged, raising all 3 gear ratios? I think it only engages to upshift from 3rd, but I'm not positive.

Even with this issue, I really like this truck

EDIT: does the trans have a separate temp sensor that prevents the OD from engaging?

 

Welcome to YotaTech. You've done a good job describing your symptoms.

I don't have your year transmission, but the manual says the O/D circuit on your truck is dead simple. http://web.archive.org/web/201408160.../6overdriv.pdf

First, O/D is an "additional gear" above 3rd. (Lock-up is another story, but I don't believe the A43D has it). Next, you should have at least two temp sensors. One is dedicated to the gauge, but the ECT (Engine Coolant Temperature) sensor runs everything in the motor. Including O/D. As you can see from the wiring diagram, if your ECT sensor has failed, the ECM will not know to ground the ECT line to the O/D relay. (If the ECT sensor fails, the engine will run very poorly.) I would start by checking the relay (using your multimeter). From there, if the relay is working, you can check for continuity on the O/D solenoid (which you can do without opening the transmission).

 

Wow - thanks! Yeah, that is a pretty simple circuit.
Looking at the schematic, it does look like the OD relay. May all my future electrical troubleshooting look like this (fat chance).
It the ECTs (both of them) are on the inexpensive side, I might proactively replace them, just so I know they work.

I'll put the rear on jack-stands so the trans can free spin the rear wheels to fake road conditions where the overdrive would kick in. For safety, I'll take the rear tires off to prevent a Ferris Bueller style train-wreck.

I know some people are a bit gun-shy with electrical troubleshooting, so If someone else has this issue and wants to verify the overdrive relay works, these are the 2 steps I'm going to do:
1) verify I have 12v between pin 2 and 4 on the relay when the OD switch on the shifter is engaged - this indicates the relay coil is getting juice.
2) with the OD switch still engaged see if I have 12V between pin 1 to ground - this is the voltage the relay sends to the OD solenoid itself.
all this being done with the real wheels spinning so the trans thinks it's time to kick in the OD.

The engine was running a little rough, but the plugs were... well horrible, and there was a visible crack, and visible connector corrosion in the dist cap where it connected to the coil.
I'm sort of dumbfounded how this truck passed a CA smog check with these issues, but... ¯\_(ツ)_/¯

I've only had OD on a light commercial cab-over diesel work truck, but from your description, I think this was actually the lockup you described: regardless of the gear you were in, turning the "overdrive" on or off changed the engine RPM for a given speed. I always visualized this as an additional gear that would shift all the gear ratios - but posts here sounded more like an "additional gear" so thanks for confirming that.

My thanks again. I'll post back my findings for posterity once I exhume my multimeter and check this.

 

Proactively replacing an O2 sensor can be called maintenance, but temp sensors should last the life of the vehicle. So whether or not you replace them, you ought to test them to give yourself some idea of where you're going.

This is the procedure for a 1993: http://web.archive.org/web/201311071...40engineco.pdf Since you're only talking about a NTC (Negative Temperature Coefficient) resistor, I'll bet yours are exactly the same.

Ferris Bueller is the apt comparison, so before I set up the driving simulation, I'd at least verify the relay is working and you have continuity through the solenoid. If I got that far, before I tried running the vehicle on jack stands I might disconnect the O/D solenoid, and run a set of wires into the cabin so I could manually switch it in and out while driving down a very-uncrowded road.

 

I just got off the phone with my wrencher friend, and he too suggested I do some electrical checks before jacking.

I've had more than one failed temp sensor - but these were also not high quality vehicles, so likely lousy quality. From what you are saying, the pickup temp sensors are better, so I'll put those last on the list. Pretty nice to have a chart showing exactly what the resistance should be for a given temp. I too would put money that these temp sensors drop resistance as the temp increases. As I understand it, it just isn't possible to design an oxygen sensor that isn't going to barf out at 80k - 120 k

The OD relay is that big blue block mounted on the pedal bracket just to the left of the brake peddle, in the foot box?

I have to say I love the idea of running a temp test signal right to the OD solenoid with the relay disconnected - if it works, I know the solenoid is good. I'm also bypassing any safeties built into the system that might be there to prevent damage... do I need to be at a particular speed before I manually engage the OD solenoid? Do I need to be on the freeway at cruising speed, or can I do this in a back road at low speed, where the trans will not be in the highest gear? I'm in the Bay Area in CA, so low traffic roads are scarce where I could get up to freeway speeds.

 

Update: I decided to hook up a wire to terminal 1 of the OD relay in this diagram; http://personal.utulsa.edu/~nathan-b.../6overdriv.pdf This is the terminal that connects to the OD solenoid. What I found is 12V sent to the OD solenoid whenever the OD switch on the shifter button has the OD enabled. So the issue has to either be with the solenoid itself, the wiring to it (including the connector to the solenoid), or a problem with the valve the solenoid actuates.

Next step will be to verify 12V to the OD solenoid itself, then test that the solenoid actuates (I've read you can hear it actuate).

There are a few decades of grime on the underside of what must be a transmission, so I'm done for today. Tomorrow morning I'll pressure wash the area where I think the OD solenoid is located so I can test it.

In case it is shot, I looked online for a replacement OD solenoid - and I have not been able to find one. But I just want to take a second to thank all the yutzes who put up adds for this part so they can state they are out of stock indefinitely. It's so helpful to advertise for parts you don't have available so my search results are chocked with useless results - that really warmed my heart.

If anyone here knows where I might obtain an OD solenoid for an A43D transmission, I'd love to get a lead.

 

Oh, I donna know, just spit-ballin' here: did you think of trying a Toyota Dealership?
There are plenty; the one I've ordered from is https://toyotaparts.lakelandtoyota.c...oid-8542022080 If I put in all the right specifications, Lakeland thinks you need a 85420-22080. Putting that number into Google, turns up https://www.ebay.com/itm/331706118253 You can gauge your own experience with eBay.

Good luck!

 

In general for common cars/trucks where parts tend to be very available, the dealership is my last choice due to expense, (unless it it one of those parts that there is no good aftermarket option). That said I know they also have the best availability. I was holding out - but honestly the price in that link does seem reasonable. Thanks for the link. For whatever reason, I had jotted down PN 85420-22060, which is the part I could not find - but it might be 85420-22080. I'll check out toyotaparts.lakelandtoyota.com search engine to see if I can figure out what's off.

I've found ebay pretty hit and miss - it very much depends on what I'm looking for. I found a good deal on a ignition, doors, gas lock keyset, and a stock jack + lug/crank toolset. Also cheap light covers all around - I picked this truck up at an insurance auction, where all my lights were busted/missing/cracked, so I need an official safety inspection (which is pretty much tires, lights and brakes) so I car re-register it with DMV.

In any case, the underside of my truck, including the trans, really does need to be cleaned before I'm going to get anything done, so I figured driving it up on my ramps while I still has light, so I can pressure wash it tomorrow morning seemed like the way to cap off my day.

 

OK, Toyota PN 85420-22080 they are calling the "Automatic Transmission Control Solenoid." Is that the same as the OD Automatic Transmission Control Solenoid, or are those the ones inside the transmission? The OD solenoid I think might have failed is accessible externally just above the pan on the drivers side.

I'll probably need to call. They don't have an image, so I'm not sure, but I'll keep investigating. I might just order the part if they have a reasonable return policy, and see if it is the right one.

 

Also, in case anyone in the future using this thread as a reference, there is a link posted https://web.archive.org/web/20140816.../6overdriv.pdf that includes a procedure to test the OD relay that in my opinion has some bad wording.

in the procedure it has
{quote}
(c) Apply battery positive voltage to the relay terminals
2 and 3. Using an ohmmeter, check that there is no
continuity between terminals 1 and 2.
(d) Apply battery positive voltage to the relay terminals
2 and 4. Using an ohmmeter, check that
{quote}

This is a little confusing to me, because nothing is going to happen if you apply the same positive voltage to pin 2 and pin 3/4 because there is no complete circuit. You will just have very lonely electrons with nowhere to go, even though they are under pressure.

I would have worded this:
{quote}
(c) Apply battery positive voltage to the relay terminal
2 and ground terminal 3. Using an ohmmeter, check that there is no
continuity between terminals 1 and 2.
(d) Apply battery positive voltage to the relay terminals
2 and ground terminal 4. Using an ohmmeter, check that
{quote}

That will allow for a complete path of current through the relay coil, which is the point of the test.

 

I pulled off the OD solenoid today and it failed the bench test: there is an open between the terminal and body, so there isn't continuity in the coil.

I'll call the dealer about the part tomorrow. Now that I know what the OD solenoid looks like, the 85420-22080 solenoid isn't the right one - I think it is one of the other shift solenoids inside the transmission. Hopefully I can get ahold of the right person, who can track down the part.

 

Be sure to have your VIN ready when you make that call.

 

I struck out at the dealer - they said they don't have the solenoid, they cannot order it, and they are not going to have them available in the future. The did give me 2 part numbers:85420-20050 and 85420-28020 - so I will give those a shot. Other than that, I will be reduced to rolling the dice at the junkyard.

I was pretty surprised - this is the 1st time I could not find a part from a dealership

 

You might have some other options. The bypass plate appears to still be available. The Volvo solenoid may still be available, but it uses a different connector. https://www.yotatech.com/forums/f116...-blues-290109/ I did find this:https://vp-autoparts.com/en/artiklar...0_aw71-98.html and https://www.ebay.com/itm/274940399713

 

I did some research online, and did find out about the bypass plate and the Volvo solenoid. I pulled the old connector - one of the bolts holding down the connector was very difficult to get at. I tested voltage at the conector, and found nothing - so there is also a break somewhere between the relay and the solenoid connector.

Spicing in the old connector isn't an issue, once I have a solenoid that works.

In the meantime I ordered the bypass while I trace the break. Once I can get continuity from the relay to the connector, I'll resume the hunt for a solenoid. As you mentioned, the Volvo one looks promising.

 

I have an '86 automatic. Only 50k miles. After about 20 minutes on the freeway (in overdrive), it shifts back to third gear and the OD relay starts going nuts. Clicking on and off like an injured cicada. I must be related to temp right? But it doesn't coincide with engine temp, just freeway time. Maybe transmission temp? It definitely has a trans temp sensor because there's an indicator light for it on dash. (it used to be a huge RV). Thoughts anyone?? Thanks! -Dante