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Can an ecu be programed if the check engine light does not

Customer Question
light with the key on?...
can an ecu be programed if the check engine light does not light with the key on?
Submitted: 4 months ago.Category: Toyota
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Answered in 43 minutes by:
8/4/2017
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago
Ted Ritter
Ted Ritter, Toyota Master Tech
Category: Toyota
Satisfied Customers: 4,487
Experience: Toyota Master Tech, ASE Certified
Verified

Thanks for posting

what year and model is your Toyota?

does the engine start and run?

has anything been tried to fix it?

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Customer reply replied 4 months ago
2003 highlander. No start. No check engine light with key on. No batt light either. 2 used ecm's same symptoms
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

Thanks for the reply

If the check engine light doesn't even turn on the computer is not getting voltage to operate. Is it a V6 or 4 cylinder?

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Customer reply replied 4 months ago
V6
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

T​hanks, I'm going to look at a wiring diagram. when turning the key on do the other dash lights turn on? do you have a volt/ohm meter/

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Customer reply replied 4 months ago
other lights come on. Yes i have a meter
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

w​ith the key in the ON position measure the voltage at one of the coil packs that you can get to, disconnect the electrical connector and measure voltage at the black/red wire, there should be 12 volts.

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Customer reply replied 4 months ago
I checked it with a test light and it had votage also checked injector it had voltage
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

S​orry, it's almost impossible to diagnose this without having some diagnostic code information, without the CEL turning on I doubrt very much a code reader will even communicate, other than checking basic voltages to the ignition system and EFI system there's not much I can do. This going to be time consuming and I would recommend that you get a factory service manual and check components like crank and cam angle sensors, computer terminal voltages and so on.

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Customer reply replied 4 months ago
i am not with the car right now. it will be Monday before i can get to it. will it be possible to call and talk with you then? i have been trying for 3 weeks to fix this. i am retired now, but worked as an auto mechanic for 50 yrs. this is my wifes car, so the pressure is on. i need HELP! i have a lot of questions. texting with fat wore out fingers is not easy.
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

A phone call won't be of much help, this is just too involved. You can try connecting a diagnostic code reader to the DLC port inside the car and hopefully it may communicate with the on board computer even though the light is not on. You can check the computer ground wire connections, the are brown/black wires and check the computer supply voltages and see if something turns up there if the code reader comes up with nothing.

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Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

Hello, I just want to post another follow up to let you know that I'm willing to try to help with this a little more when you are ready to continue, maybe we need to find out some basics like is it losing spark or fuel or are the fuel injectors even working.

Please check the following:

spark to the spark plugs

fuel supply to the fuel rail

injector pulse voltage

timing belt timing

If we know what the engine is missing in order to run we can concentrate more on that.

Looking forward to hearing back from you.

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Customer reply replied 4 months ago
Thanks Ted. I will be at the car on monday. I will recheck the power and grounds. I also want to check the batt light circuit. Maybe diode trio issue. ???
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

Sounds good let me know what you find about the things to check.

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Customer reply replied 4 months ago
Good morning. Trying to find j/c 7. A ground junction right side of dash.
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

Hello, I'd like to narrow this down a little, I have a feeling that it is not getting spark at the spark plugs, can you verify this before we go any further.

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Customer reply replied 4 months ago
No spark
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

Ok, I'll look at a diagram and go from there, .

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Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

Please look at the label under the hood and verify which engine it has, I think it's the 3 MZ-FE or 1 MZ-FE

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Customer reply replied 4 months ago
1mz-fe
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

with the key on you had voltage to the black/orange wires at the coils and the injectors, is that right?

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Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

If there is voltage there check the B+ terminal in the check connector under the hood.

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Customer reply replied 4 months ago
Ck connector?
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

There is another diagnostic check connector under the hood, should be near the firewall on the pass side, open the cover and see if there is voltage at the B+ terminal.

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Customer reply replied 4 months ago
When I was checking pins at the ecu, the e8-17. Brown wire is not a good ground.
Customer reply replied 4 months ago
I do not see this connector. Does it look like the ones they used 20 years ago?
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

Let's just do this, pull the EFI main relay out, in the fuse box under the hood, turn the key on, two of the terminals must have 12 volts, check and let me know.

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Customer reply replied 4 months ago
One has 12, one has 10
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

Too much of a drop, some resistance in possibly the ignition switch, does the EFI fuse have 12 volts on both sides?

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Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

Measure at the top of the fuse metal tab

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Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

Also check the 10 A gauge fuse on the inside,

Unfortunately I have to go offline foe a couple of hours now, we're making some progress and we should be able to wrap this up when I get back, let me know avout those voltages and fuses.

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Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

Back online.

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Customer reply replied 4 months ago
Thanks for your help. After being on my knees all day, I am tired. It may be a day or two before I can get back to it. Tomorrow is doctor day. 3 appointments. While I was testing, the check light came on, so did the batt light. When I started looking, I found that the e8 plug at the ecu was not tight. When i connected, the lights went out again. I decided to scan the system with the e8 unplugged, I was able to communicate. I may be over thinking it. I did this with two ecus. What do you think ? A component or circuit. In the e8 plug?
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

T​he whole problem may be right there at the ecu connectors, check them for loose fitting connectors or grounds, remember all ground wires are brown/black tracer, they have to be grounded to the body.

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Customer reply replied 4 months ago
Ok. I will keep checking. It may be a day or so.
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago

A​ll right, talk to you then.

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Customer reply replied 4 months ago
It's me again. I have rechecked the gods and . 12 volt feeds. All ok. The only clue if I unplug e8 or e7 my ck light and batt light will come on. I am able to communicate with scanner at this time. I got codes, but they deal with components on those connectors. This happens on three different ecus. ???
Toyota Mechanic: Ted Ritter, Toyota Master Tech replied 4 months ago
I'm away from y computer now I will get back to you tomorrow
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