Check Engine light....what check engine light

Hello all,

New van owner here. I recently purchased a 1984 automatic 2WD. It came with a blown head gasket which I repaired and its up and running for the most part. I bought the van as a project for $600 including some spare parts and some helpful items like new tires. I guess I have a spot in my heart for these vans. Yes I am a glutton for punishment I suppose! That being said, these vans are cult classics here in SoCal for surfers due to the large capacity to hold boards and other gear. The HG repair was not too bad, I had a 2nd person so that helped quite a bit, took 2 days, one day tear down, one day assemble. I hope to post more on that a later time.

So the van is running, I've driven it around town for about 30 miles since the HG repair. In preparing for California smog check I looked to see if my check engine light (CEL) was working, also attempted to read ECU codes. Low and behold I did not see any CEL even during key on. This led me to remove the instrument cluster and check the bulbs, as I suspected the previous owners had removed the CEL bulb, socket and all. While waiting on a replacement light socket (Toshiba 2V for anyone who needs on at $2.99 Each) I moved over another light and socket from a less important function (I used the low fuel instrument light into the CEL position). Ok, now I get CEL and it wont clear, stays on when the van engine is running. So I attempt to read codes .... jumping the test connect (the 2 pin/wire connector) I get no codes , only constant CEL illuminated, does not flash or clear or change, constant on. I've tried different sequences to the test jumper, jumper before or after key on, placed auto trans in neutral, no change-just constant CEL illuminated. I confirmed that at the test connector I do see approx. 4.8V across the pins, I also confirmed that ground pin of the pair has continuity to ground. These pins look like a pull-down as you ground T to E I believe so my test harness seems to be connected to the ECU.

Any ideas here on what prevents me from reading ECU codes? no blinking no codes, just steady CEL illuminated...

The TPS was mated , In further troubleshooting, I also tried disconnecting the TPS and am thinking about installing a new TPS which I probably should have done when I had the TB off for repairing the HG (should have, would have). Is there something in the ECU software that would prevent displaying codes if the throttle-body position is incorrect? Van odometer says approx. 123K miles.

Hoping its not a bad ECU and Thanks in advance!

Assuming you got the CEL light hooked up to the correct leads, it sounds like a failed ECU. Now that these vans are getting over 30 years old failed ECU's are not uncommon. On 84 - 85 vans there was only one used (Toyota #89561-28010). In the past I've been able to find these fairly cheap on eBay. They have some there now, but the prices they are asking are way bit high ($200+). Perhaps watch craigslist parting out ads, or maybe your local salvage yard? Good luck. Tim

Quote:

---

Originally Posted by timsrv

Assuming you got the CEL light hooked up to the correct leads, it sounds like a failed ECU. Now that these vans are getting over 30 years old failed ECU's are not uncommon. On 84 - 85 vans there was only one used (Toyota #89561-28010). In the past I've been able to find these fairly cheap on eBay. They have some there now, but the prices they are asking are way bit high ($200+). Perhaps watch craigslist parting out ads, or maybe your local salvage yard? Good luck. Tim

---

Thanks Tim!

The plot thickens (somewhat)... here is my ECU
Attachment 3435

Note that the vehicle year is 1984, the engine of course is 3Y and that is what the valve cover indicates on the engine 3Y
So the ECU has what looks like 'parts guy' writing that says '87 TOY VAN' however it is stickered as Toyota 3Y EC.

Any idea what a 4Y ECU would do in a 3Y van? (if it really is a 4Y ECU)

By the way , for anyone else removing the ECU here is a photo of the where it resides on the vehicle. I had to remove the drivers seat belt take-up reel. The ECU is held by 3 fasteners, one nut at the top end of the ECU and 2 sheet metal screws which attach near the connector face. You can see the bottom of the ECU just poking out where the yellow connecters mated to the ECU were removed.


Attachment 3436


I'll look around for ECUs or even make an attempt at repairing this one and if successful posting a thread.
By the way, the ECU location near the door jamb makes me suspect these units see the mechanical shock of over zealous door closing. So circuit board or printed wiring board fractures or broken solder joints might be the culprit on many an ECU.

Whoever marked-up that ECU was wrong. That ECU was only used on 84 - 85 Toyota 3y vans. Starting in 86 Toyota switched to the 4y & upgraded from vacuum advance to electronic. At that point the ECU's became more complex & required an additional wire harness port.

Other than hack mechanics rewiring things, it's my belief that time & humidity is usually what kills these. This is particularly true for vans that become disabled & get parked outside for extended periods. Most of the bad ones I've diagnosed were good when the van was parked, but became bad sometime during a long slumber. Good luck with finding a replacement. Tim

On to phase two of check engine light...

300 to 200 bucks for a new ECU! I can get pretty creative for 200 bucks especially since this is a project car for me. this may not be worthwhile for everyone.

Here is the ECU inside, access can be made by removing the screws at the 4 corners of the unit, both top and bottom covers to allow access to inspect both sides of the board. (note this is not for the faint of heart or without electrical skills of some level) a failure to correctly modify or repair the ECU can leave you stranded!



Carefully inspect both sides for any obvious signs of component damage. Often capacitors will be bulging or look for discolored traces.


heres what I found

Attachment 3437


you can see the discoloration where gases exited the part and of course the fractured transistor case.

That explains the CEL! yes you were correct Tim!

D571 is the part number of the part (on the other side) $3.90 on ebay

Nice write-up and thanks for the excellent pics. I haven't tried to fix a TV ECU yet, but I have spent time repairing Pinball machine boards & some inverter/power supply PC boards. Most of the pinball boards I worked on were from the 80's - early 90's and I had a high success rate. Since your ECU is also from the 80's, I'm thinking you might very well be successful. Modern electronics for inverters and switching power supplies are a completely different story. I pretty much don't even try to repair those anymore. After replacing the obviously damaged components (like your transistor), I've experienced exciting spark showers & blown breakers when re-energizing/testing. Not sure why that is, but suspect the parts that blew were only doing so because of down-stream short(s). As you might guess I have not been trained in electronic repairs, so I'm a bit ignorant. I'm just a curious guy who takes things apart and repairs/replaces parts/components that are obviously damaged (like swollen caps and smoked transistors). I also used to repair burned traces by jumping/soldering small wires across them. I stopped doing that on some appliances as repaired boards can fail quite spectacularly (potentially dangerously) during a future surge or other part failure.

I fixed a microwave oven once by soldering wires across multiple smoked traces on the backside of the touch-pad board. It worked great for about 3 years until we had a power surge. My wife was in the kitchen at the time and there were literally flames shooting out the front of the touch-pad :shock:. In hind site it dawned on me that PC board traces are like little fuses. Soldering wire across them is like replacing .5A fuses with 20A ones. As long as everything works like it's supposed to, you're golden. But when something unexpected happens, damage & danger can become unpredictable. Not to suggest you're going to do anything like that, just saying. Good luck with your repair. I hope it works. Please keep us posted. Tim

Glad you investigated and it can be fixed for so little!
I am sad to say I think my ECU is suffering an affliction as well, although the symptoms are different(Hesitation in first 15 minutes at low RPM's fixed by replacing ECU) so I'm assuming it'll be a different capacitor. I was going to post on another recent ECU thread and was getting worried-what will we all do when ECU's can only be had for 100's of dollars and are dropping left and right? It seems they should be somewhat simple:wnk: and yours is an excellent example-if your fix works which I have high hopes it will!
Keep us updated and thanks for the informational post.
Aaron

Quote:

---

Originally Posted by djshimon

Glad you investigated and it can be fixed for so little!
I am sad to say I think my ECU is suffering an affliction as well, although the symptoms are different(Hesitation in first 15 minutes at low RPM's fixed by replacing ECU) so I'm assuming it'll be a different capacitor. I was going to post on another recent ECU thread and was getting worried-what will we all do when ECU's can only be had for 100's of dollars and are dropping left and right? It seems they should be somewhat simple:wnk: and yours is an excellent example-if your fix works which I have high hopes it will!
Keep us updated and thanks for the informational post.
Aaron

---

FIXED IT! The van is up and running no CEL. I'll post the details and insights in a new thread.

Sweet!:thmbup:

Awesome :dance2:.

Quote:

---

Originally Posted by dude

FIXED IT! The van is up and running no CEL. I'll post the details and insights in a new thread.

---

Would you mind posting it here? Keeping it all in the same thread keeps it more organized and easier to find. If you like I can change the title to whatever you like. Tim

Quote:

---

Originally Posted by timsrv

Nice write-up and thanks for the excellent pics. I haven't tried to fix a TV ECU yet, but I have spent time repairing Pinball machine boards & some inverter/power supply PC boards. Most of the pinball boards I worked on were from the 80's - early 90's and I had a high success rate. Since your ECU is also from the 80's, I'm thinking you might very well be successful. Modern electronics for inverters and switching power supplies are a completely different story. I pretty much don't even try to repair those anymore. After replacing the obviously damaged components (like your transistor), I've experienced exciting spark showers & blown breakers when re-energizing/testing. Not sure why that is, but suspect the parts that blew were only doing so because of down-stream short(s). As you might guess I have not been trained in electronic repairs, so I'm a bit ignorant. I'm just a curious guy who takes things apart and repairs/replaces parts/components that are obviously damaged (like swollen caps and smoked transistors). I also used to repair burned traces by jumping/soldering small wires across them. I stopped doing that on some appliances as repaired boards can fail quite spectacularly (potentially dangerously) during a future surge or other part failure.

I fixed a microwave oven once by soldering wires across multiple smoked traces on the backside of the touch-pad board. It worked great for about 3 years until we had a power surge. My wife was in the kitchen at the time and there were literally flames shooting out the front of the touch-pad :shock:. In hind site it dawned on me that PC board traces are like little fuses. Soldering wire across them is like replacing .5A fuses with 20A ones. As long as everything works like it's supposed to, you're golden. But when something unexpected happens, damage & danger can become unpredictable. Not to suggest you're going to do anything like that, just saying. Good luck with your repair. I hope it works. Please keep us posted. Tim

---

Too many modern circuit boards tend to be 4+ layer affairs, which are effectively unrepairable if anything goes bad on the middle layers.

Here are my observations on the Toyota ECU. My ECU was a1984 model for 3Y engine.
You likely need some level of expertise with soldering/desoldering to conduct a repair onyour own but it is doable and hopefully this write up will help.


Cautions, any repairs to electrical equipment should be with the batterydisconnected. A repair to the ECU could result in a failure of the entire ECU or inability to operate your van.

That being said, I was impressed with the build quality of the ECU. The boardis well laid out and uses high quality materials compared to many consumeritems you see today. The PWB material is a high quality fiberglass. All components are on one side of the board making build and testingstraightforward. All parts are through-hole and the board is only 2 layers which helps.
If you decide to attempt repair, remove the 4 screws at each corner, front andback sides. DO NOT REMOVE THE SIDE SCREWS
those screws hold in the heat sunk power supply components (only remove if those are failed). You can remove the front brackets or 'tangs' which mount the ECU into the van. No need to fully remove the board from the frame. I kept mine in the frame just remove top and bottom covers again unless the side wall mounted components are suspect. The basic board is wave soldered with the side wall parts soldered in-place once the board is installed in the frame, this is a common technique when heat dissipation is needed for certain parts.

Here is a photo of the ECU with notes


Attachment 3474

Note the power section of the board on the lower left, there is a large 3UF capacitor which is the green rectangle, along the side is the switching components. The top right of the board is the digital section with the microprocessor which uses 5V.
General theory of operation is that the microprocessor monitors the engine readings and uses a look up table stored in a PROM to set correct engine outputs. The left side of the board is the I/O with custom relay/valve drive ICs by Toshiba. Note that these parts use 11V and are no longer in production. If you suspect damage to these Toshiba parts you have no option other than parts from another Toyota ECU (perhaps other models use the same parts)?

My problem was the stuck on Check engine light CEL. I found damage to the transistors located around left of the middle. I replaced both parts with NTE293 (original was D571 which is 2SD571). The NTE293 is the equivalent part available at my local parts store. Above the top transistor in the photo is a 1Kohm resistor which supplies current to the transistor base. This was also damaged and replaced. The CEL function is controlled by the micro thru a part near the top of the board photo HD7407 which is a TTL open collector driver (this part pulls low the base drive of the transistor which controls the current thru the CEL (what is known as a low side switch)). I replaced this 7407 part with an equivalent from my local parts store. For good measure I also replaced all electrolytic capacitors on the board, these parts usually fail with age and are circled in the photo. I also replaced a ceramic cap 222k which is 220pf near the transistors as it showed some brown marks.

It took me a little detective work but I was able to fix it. I now get good CEL, and can read codes (I get the code flash for no codes). Van also seems to run much better so there may have been another issue with the 7407 part I replaced.

General troubleshooting: if you have a total dead ECU I'd start by checking the power section of the ECU. If you have an operating ECU with some issues, go to the IO section, center and left. Carefully check the boards components using magnification as some issues can be difficult to see with the unaided eye. If you suspect any of the electrolytic caps go ahead and replace them , I replaced a 47uF rated for 35V and a 100uF rated at 15V. Also one more that I cant find at the moment. These parts have polarity and the board is silkscreen shows where the - minus terminal of the part is to be located.

Good luck to others attempting similar repairs hopefully this write-up will help.

Thank you for that detailed write-up. It's nice to have an electronic guy that's into vans :thmbup:. Now I'm glad I kept my bad ECU's (I have 3 now). All marked BAD in sharpie. Those may come in handy someday for parts when these ECU's get harder to find. Tim

:whs:

Great write-up!

I don't have any bad ECUs (that I know of) ... but now I'm glad I spent a number of years employed in electronic assembly and QC in the '80s!!! :yes:

Gwen

Hi all. New to the forum and I love seeing everyone's eagerness to help. I am having an issue with the check engine light (CEL) not turning on at all even with the test connect "jump" for the bulb test. I made sure it wasn't just the bulb as I took the one from the open door indicator. Should I be checking my ECU as well?

What about when you turn the key on to the "Run" position but do not start? The CEL should illuminate solid when doing that. If not, then it's a bad ECU. Wires between the ECU and the CEL bulb could also be damaged, but that's a bit unlikely. The easiest way to check would be to swap ECU's, but you'd need to have an extra one laying around (and I'm assuming you don't). Here's a thread with more info on how to test: https://www.toyotavantech.com/forum/...gnition-timing.

FWIW, with a vehicle this old I would highly recommend having a spare ECU. They are becoming rare, but can still be found on eBay at times for reasonable prices. Tim

https://www.ebay.com/sch/i.html?_fro...n+ecu&_sacat=0

Here's a link to an article showing how to replace: https://www.toyotavantech.com/forum/...place-your-ECU

Hello everyone,

For 84-85 3Y, is the ECU the same in Manual and Automatic vans? If I find one in the junk yard, is there a way i can check if it's working?

thank you!