No overdrive/shuts off engaged at a stop. Tranny/ECU issue. Automatic.

Today’s issue of an overworked broke college student.


1996 147 K miles 2wd 2.4liter.
Truck was not engaging into overdrive/bogging and was not going over 3k rpm. Got 2 opinions 1 from a family mechanic and the other by a truck specialist and sent it out to get tranny rebuilt.
Was shifting smoother than ever and like a dream for about 100 miles .


Back to no overdrive , bogging and stalling at stops and won’t go over 50 MPH(3k RPM).
Will have it towed to the shop (reputable and well know for work) (has 12,000 mile warranty)

Could it be something else?

 

Any codes?

That's always the first question.

 

No codes respective to it bud. The only code I’ve had is 401 and it’s the manifold gasket leak that I’ve yet to fix

 

Update:
Full Tranny Rebuild has been made including replaced T/C , Test drove with the mechanic, 20 minutes into drive O/D disengaged/ Solenoid was changed with new OEM.
truck ran like Shit again and was rev limiting at 3k, wouldn't go over 50 mph, and not responding to full throttle.
Airflow is normal.
After 30 minutes CEL turned off and car returned to normal idle and O/D engaged. Ran like a dream, and the shifts were crisp and clean.
then as it started bogging and disengaged O/D , revs limited and felt like I was back to square one.
Today was able to plug in OBD2. Check engine light is on, OBD2 says cannot connect to ECU.
Had to leave car at the Tranny shop. Being as I Paid and had the full Tranny rebuild the shop says will diagnose and try to figure out the issue.

I am led to believe this is a ECU issue.
NGK Iridium Spark Plugs and wires placed 6k miles ago.
Optima Yellow 34 top Placed 2 months ago.
Oil service done 1.5k miles ago.
No auxiliary appliances.





Does Anyone have a clue what this could be?

 

It sure sounds like they misdiagnosed it NOW. Tough call before the fact. If the PCM has the correct power and grounds and there are not shorts or opens in the harness that only leaves the PCM. If it is the PCM will they buy it and put it in? If this is the problem what are they going to do about the price difference between the trans overhaul and the PCM? If they were "smart" and it was the PCM all along they should just put it in a known good PCM and tell you some BS about how they found a wire loose in the valve body and cross their fingers.

 

You know that’s what I thought at first, ( if PCM is another way to say or main component of the ECU)
Until I test drove it after the rebuild, those 20 minutes were incomparable to how the truck was before. The shifts weren’t lazy ( didn’t take forever to transition) and the truck felt a bit more responsive.
I was shown some of my old components and i was convinced that after 150k miles in my truck the rebuild wasn’t that far away. mind you I bought it with 142k
And a coworker told me the original owner was an old guy that was a painter and he would haul a loaded bed every time he saw him ( after the fact he saw me driving it) and that it was put to work.

I could say I have that piece of mind .
Am I happy about it? nah not it all
I wish I had the tools and the time and the sources ( dealer part plug) to have done it myself.

Do I blame the shop no,
I mostly blame myself out of ignorance because I run daily a phone OBD2 scanner to track the O2 sensors and my fuel rate ( being as I have a Header & cat leak) and I never had problems communicating to the ECU.

And when this first occurred the Transmitter wouldn’t connect to ECU (prompting connection was lost) and after 2 days of forum searching I was convinced it was the O/D solenoid, and felt my assumption was confirmed when my uncle said so as well(35+ years of body shop /engine rebuild/ tranny replacement) so I naturally trusted his gut.

But I didn’t think it would be ECU , because after driving a bit the first time the car went back to normal, with its usual shift points , O/D and regular idle / and the transmitter was reading everything fine then.

And as soon as the truck began to feel like it was running starved/ rev limit/ limp home at 50mph the transmitter wouldn’t connect. Very sluggish to say for a fact , the trucks grunt and are slow but are in no means slugs compared to 90s diesels / and it was more sluggish than those.

To my ignorant self The solenoid seemed like a good enough explanation and I didn’t think of it twice (I’m a fool) .

But now I feel certain to begin with it was ECU issues , and the tranny rebuild wasn’t needed exactly then and there but eventually in the coming 30k miles maybe it would’ve.
Now I want to see how this is going to go in regards to what the shop wants to charge for sourcing a refurbed ECU, because I’m looking at $170-350 at them.
And if I’m adventurous enough ill yard hop to find a low mileage one under 120k

But I’m not irate (I am Ifeeling incredibly ignorant and naive) because I plan on riding this truck out and making it a project as soon as I upgrade back up to a newer gen after my second gen was totaled (it was parked).



Whoever can teach me anything about this, or want to leave your two cents, just add in.

 

Ecu’s are pretty finicky, do I think you’re ecu maybe bad yes, but I would check as many wires as possible. Harnesses do short out, and you might not know it but our computers are quite dumb, in fact a Denso engineer told me that specifically, so you could have a short that could f@&$ up your new ecu. It’s not impossible to ohm every wire but it’s a real pain. Going through that trouble will give you piece of mind so you don’t just wind up throwing parts. Anyone with the FSM wire diagram should be able to check that, I don’t have one but maybe someone will post the ecu section of it, or go to Toyota.

 

It sounds like the ECU is going into fail-safe mode. This is when it detects a problem with a sensor and adjusts things like ignition timing, injector pulse, shift points, etc. to allow the engine to at least run a little. For example if the MAF sensor stops working the engine has no idea how much air is going in, so it just dribbles a little bit of fuel in and doesn't advance the spark just so the engine will at least run.

It could be a sensor problem, or there's a problem with the ECU where it isn't processing the input from the sensor correctly. The Toyota Repair Manual lists the fail-safe mode (how the ECU adjusts) for each sensor, so you might want to check which sensor's fail-safe mode results in your symptoms. Some sensors have more drastic fail-safe modes. For example, with a bad coolant temperature sensor the ECU just assumes the coolant is at 180F which doesn't affect driveability very much once the engine is warm. The MAF and throttle position sensor have more drastic fail-safe modes.

 

That’s the stage the shop is currently at.
And my anxiety is a bit high being as I don’t know what to expect out of a negative result or if they are going to charge me crazy man hours.

I am pretty new into learning about how these simple electronic engines are assisted .
Thank you, @Luv my yota

 

@DrZ

You have informed me more about the electronic intelligence of this truck than I believe I would be able to dig up in 3 years . I really thank you for this and I believe that message should be stuck high up in the Gen 1 column for any other newbie like myself that can be wondering the same thing.

Now let’s say I have harness failures, would it be to Change these specific connections or being as it’s a older truck should all of the important connections be replaced?

If this was a rating scale of 1-10 on how much I know about electronics I’d be at 1.3 and that .3 is thanks to you .

 

Did they check to see if your cat was plugged or partially plugged up? It'll cause almost every issue you listed and the miles are about right for it to fail.

 

Yea completely disconnected during the test drive, airflow is normal.

 

Just a thought I had earlier today about your ecu. Does it rev to redline like normal in neutral? If so you can rule out ecu and it could be trans or wiring to trans.

 

Hopefully the trans is now fixed by the shop.
For future posters,
Try shifting/driving the trans manually in each gear.
Stalling sounds like an engine management thing.

 

No when in neutral it limits and bounces at 3.1k
Normally she would reach redline and bounce

 

I did so , o/d wouldn’t engage and even spamming the O/D toggle button .

And they are still looking into it.
Don’t have it back yet.
In the meanwhile I’m using a pressure cooker Corolla in the meantime.


Still wouldn’t change that the truck is running like shit ( like if it was starved)

 

i agree to look at the converter closely , with a vacuum gauge in the upstream o2 sensor hole, before converter, goose throttle to 3-4 k rpm. there should only be 1-2 psi backpressure.
converters can fail when hot and do ok when cold. if the pressure is high and you have a downstream 02 sensor, after converter, do the same there. if its low you know the converter is blocked. if its still high, problem is further down the exhaust.

 

i also saw that you had a manifold leak. i assume this is a exhaust manifold. even though you hear it leaking externally, it also sucks in unmetered air and can damage a converter.
intake manifold will also kill a converter.

 

That was already diagnosed by the shop.
Airflow is optimal .

 

Update , the ECU is the Culprit ,
just got called from the shop,
They are charging me charging me $360 for the whole replacement with a refurbed ECU.