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1997 Sidekick JX 16V 4x4
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Discussion Starter · #1 · (Edited)
When I bought my sidekick the check engine light was on and I found codes P0122, P0450, and P0510. After clearing them P0122 is the only one to return, but it returns immediately on startup. The previous owner told me the check engine light was on "for some emissions thing" and his brother who is a master mechanic couldn't figure it out. The owner took good care of this rig and used it to deliver car parts for his small town parts store he's had for 20+ years. I don't think he was trying to pull a fast one on me, he just didn't understand what was wrong and the CEL didn't bother him enough to really dig into it.

This thread has given me motivation to finally tackle this once and for all (posted there and @Bex advised me to start my own thread):

I used this page as a starting point in my latest attempt to figure this out:

From that page, I've determined that the TPS is not getting the 5V ref on the Grey wire with Red stripe. From this forum I found info saying there's also a Grey/Red wire feeding the MAP sensor with the same 5V ref.

I have essentially no voltage (0.02V) at the TPS, MAP, and the ECU on that Grey/Red wire. I found a spot a couple inches from the ECU connection where the Grey/Red wire has rubbed against something and the wire strands were showing. I clipped that and verified I still don't have voltage (well, 0.02V) at the ECU. One note, it looks like someone has tried to removed the Grey/Red pin from the ECU connector in the past. I can see tool markings around the pin like someone was trying to release the tab that holds it in.

I've read on here about ECU's and bad capacitors, and that the 5V ref is fed from a bus that also serves other circuits. What's next? Check for 5V on another circuit fed by the same source?

EDIT: I've also read that a different shorted sensor fed by the 5V ref could trip a safety feature in the ECU and cause it to not output the 5V. That's why I was thinking test for 5V elsewhere. Seems like people say to unplug the sensors one by one and look for the one causing the problem?
 

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91 sidekick 4dr 4x4 16v 1.6l manual transmission (mpi)
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God speed there Mr Snerksky

You jacked my thread so I’m gonna jack yours real quick...

Can anybody tell me exactly which sensors are involved in that stupid 5v ref circuit???? I had my 5v come back for the same tps wire.. unplugged the o2s maf uh the temp one...all the ones I thought are in that 5v ref circuit. Then rewired the tps and I STILL lost the 5v out of the back of the ecu after a day or two. And Ive Got good power and ground to the ecu🤷‍♂️🤷‍♂️

I’ll try n help you a lil here Snerk. I’d pull all the involved sensors off first and watch for your 5v tps wire to come back up. If not then I’d pull all wires out of the back of the ecu that are involved in that 5v ref circuit test each of them as you pull them out one at a time for stray vol in case they’ve shorted to a power wire. If all normal then reset the ecu....I had a bad maf sensor that shorted out and was sending high vol back to my ecu..... If your 5v comes back now out of the back of the ecu it should be a sensor wiring problem at that point. Granted you check the power and ground on the ecu. Next add each set of wires back to one sensor at a time and watch your 5v to see if it drops. If it does then bingo.. got your bad wire and can rerun or whatever.

Hopefully you’ll find something. I found my bad maf but still isn’t my problem🤷‍♂️

Wouldn’t hurt guess to load test each wire before you added them back to the ecu jus n case. Guess you could go back thru n do that if you didn’t find anything on the first round there.

Good luck!! I’m still holding out that mayyybe I can fix mine. Gets expensive when your ecu won’t put out the 5v ref anymore I’ve got a fsm for I think same as yours if you need any info
 

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While the issues may be the same, be reminded that Snertsky is OBD2 and Yukon is OBD1. That being said, on the OBD2 vehicle, it appears that the grey/red provides the 5v reference to the MAP, TPS and fuel tank pressure sensor. From what I understand - and I’m no expert here - this issue can be caused by a short in the circuit of any of the sensors connected with the grey/red wire causing the ECU to drop the voltage, or the ECU itself.
The OBD2 electrical diagrams are here:
One potential idea would be to disconnect the sensors that run off the 5v circuit, and see if you then regain the 5v reference at the ECU itself, to check whether the issue is a short in one of those sensor circuits that is causing the issue. Others here may have some better ideas (particularly Fordem and Aqua). Otherwise, to get some real help, I’d post over on Rhino’s forum here. He‘s beyond expert with this:
 

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There are 5v voltage regulators in the ECU that converts 12v to 5v for internal logic components and external sensors. My first thought was if you found your 5v ref wire to the TPS to be frayed, it's possible it shorted out to chassis ground which likely would have zapped the ECU 5v regulator to the sensors. Thus, the source of the problem would be internal to the ECU. The 5V regulator is a cheap device requiring someone with soldering skills to replace it. A few bucks plus less than an hour of labor. I don't know if there is anybody that repairs ECUs. Perhaps someone on here has more knowledge on ECU repair than I do. Regardless, good luck getting it fixed.
 

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1997 Sidekick JX 16V 4x4
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Discussion Starter · #5 ·
I found the same info as Bex saying it's just the TPS, MAP, and Fuel Tank Pressure Sensor using that ref voltage. I will unplug all those and verify I still don't have 5V.

I had the same thought that a frayed wire could have shorted and fried something.
 

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It would be unusual for the 5V regulators to fail in the ECU as they are pretty bullet proof. Unfortunately the only way to tell is remove the wire from the ECM coupler and back probe the terminal.

or..

cut the wire just out from the ECM (like where its rubbed as you need to repair that anyway) and measure there. If you have volts, the supply is good, start tracing the next rubbed thru shorted spot.
 

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1997 Sidekick JX 16V 4x4
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Discussion Starter · #7 ·
It would be unusual for the 5V regulators to fail in the ECU as they are pretty bullet proof. Unfortunately the only way to tell is remove the wire from the ECM coupler and back probe the terminal.

or..

cut the wire just out from the ECM (like where its rubbed as you need to repair that anyway) and measure there. If you have volts, the supply is good, start tracing the next rubbed thru shorted spot.
I already snipped the wire where it was frayed and that's where I'm testing from.

Unfortunately I don't have any voltage even after disconnecting all the sensors. I found a plug in the LR tail light access hole that has the Grey/Red and Brown/Red wires for the Fuel Tank Pressure Sensor and unhooked it there. Would it be worth my time to disconnect all the wires going to those sensors from the ECM harness plug?

I'm having some difficulty removing the Grey/Red wire from that plug. I got the little latch opened but couldn't figure out the prong inside. Tired of laying on the floor board. Any tips?
 

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1997 Sidekick JX 16V 4x4
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Discussion Starter · #8 ·
I should note the thing seems to run fine. I think it must be in "fail safe mode"? The previous owner drove it this way the whole time he had it.
 

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91 sidekick 4dr 4x4 16v 1.6l manual transmission (mpi)
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Ha your lucky then. Mine won’t run worth a crap

Didn’t realize he was all the way into the obd2

Those ecu connectors are a pain. Took me looong time to figure that one out. I used a needle probe on my tester. Could prob use a paper clip. Slide it right along the top of the little hole keeping pressure against the top of the hole till you get to the back of it and then push down while pulling on the wire gently. Once you get it it’s easy but a pain to get it the first time.... I like pulling it out of the harness At the ecu then you completely eliminate any shorts in that wire.
 

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91 sidekick 4dr 4x4 16v 1.6l manual transmission (mpi)
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Hey Snerk

One more quick.. you had that grey red frayed...my ecu would take awhile.. like days sometimes with the battery unhooked for that 5v to crawl back up to 5v. Mayyyyyybe it shorted and a reset of the ecu would bring it back if that fray on the grey red was your only prob🤷‍♂️
 

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I already snipped the wire where it was frayed and that's where I'm testing from.
Where did you snip the wire? Yes, I get that you snipped it where it was frayed, but where was that - unplug the harness from the ECU and use a continuity tester to determine whether or not you have continuity between the connector and the "snip point". Do you have continuity between chassis ground and the "snip point" - if the ECU and the sensors are disconnected you shouldn't.

Once you've established that you have continuity from the point where you're attempting to measure (the "snip point") and the ECU connector, and no continuity to chassis ground - if you don't have the 5V ref with the ECU connected, then the problem is internal to the ECU.
 

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1997 Sidekick JX 16V 4x4
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Discussion Starter · #12 ·
Where did you snip the wire? Yes, I get that you snipped it where it was frayed, but where was that - unplug the harness from the ECU and use a continuity tester to determine whether or not you have continuity between the connector and the "snip point". Do you have continuity between chassis ground and the "snip point" - if the ECU and the sensors are disconnected you shouldn't.

Once you've established that you have continuity from the point where you're attempting to measure (the "snip point") and the ECU connector, and no continuity to chassis ground - if you don't have the 5V ref with the ECU connected, then the problem is internal to the ECU.
The wire was frayed a couple inches from the plug in the ECU so that's where I snipped it. I do have continuity on that short 2 or 3 inch section to the connector. I do not have continuity between the Grey/Red and chassis/ground anywhere. I checked at several spots.

While I was poking around under there, I noticed the ECU has some handwriting on it and a date from 2007. I think someone has been in there before.... Sounds like I need to repair my ECU or find a used one?
 

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worth pulling the ECU and checking the capacitors on the 5V rail, its always possible one has dried out. Just because they aren't Rubycon ones doesn't mean they can' fail. Any decent electronics tech should be able to find the 5V regulator circuit and check it over.
 

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I already snipped the wire where it was frayed and that's where I'm testing from.

Unfortunately I don't have any voltage even after disconnecting all the sensors. I found a plug in the LR tail light access hole that has the Grey/Red and Brown/Red wires for the Fuel Tank Pressure Sensor and unhooked it there. Would it be worth my time to disconnect all the wires going to those sensors from the ECM harness plug?

I'm having some difficulty removing the Grey/Red wire from that plug. I got the little latch opened but couldn't figure out the prong inside. Tired of laying on the floor board. Any tips?
Disconnecting the 3 sensors (MAP, TPS and fuel pressure) should break those 3 circuits. Are you saying that when those sensors are disconnected, now you have NO voltage at the ECU connection at all, rather than some voltage but just not 5V??
 

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Ha your lucky then. Mine won’t run worth a crap

Didn’t realize he was all the way into the obd2

Those ecu connectors are a pain. Took me looong time to figure that one out. I used a needle probe on my tester. Could prob use a paper clip. Slide it right along the top of the little hole keeping pressure against the top of the hole till you get to the back of it and then push down while pulling on the wire gently. Once you get it it’s easy but a pain to get it the first time.... I like pulling it out of the harness At the ecu then you completely eliminate any shorts in that wire.
Yukon, I see from other forums that you’ve been dealing with this for quite a while. I really do suggest that you go over to Rhino’s forum, post your ECU model number, and explain your problem. Rhino will be able to help you.
 

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1997 Sidekick JX 16V 4x4
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Discussion Starter · #16 ·
Disconnecting the 3 sensors (MAP, TPS and fuel pressure) should break those 3 circuits. Are you saying that when those sensors are disconnected, now you have NO voltage at the ECU connection at all, rather than some voltage but just not 5V??
Originally I was showings 0.02V on the Grey/Red wire, but I chalk that up as no voltage. I have all of the sensors disconnected and still have no 5V ref. It's sounding like I need to dig into the ECU.

I found this fixkick page and can see the diode he's referring to in the image.


I checked the grey/red wire for continuity to ground (shorting) in several spots and didn't find anything. I'm a little nervous there's a frayed spot somewhere that would short the 5V ref and cause this same problem again if I get the ECU fixed. It may not be grounded now but maybe some bumping around in the woods would create continuity. I had another thread about my tail light wiring loom not getting power to the RR lights and found the loom had rubbed against some other wires and wore through some wires. Pics can be seen here:


It sounds like I'll be better off on rhinopower for this ECU issue? I've never been there before. I'm willing to learn and post results (eventually).
 

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Personally, I would post over with Rhino....at least to get the confirmation that D108 is the correct component you should be looking at. Rhino ONLY deals with ECU‘s - he’s been a member of this forum and incredibly knowledgable. Have the model number of your ECU, and post on his forum (IMHO)...and if possible, maybe link your post over here, so that those who have similar issues can follow along. Just my opinion.....
 

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And with regard to your situation with the tail light wiring harness....how did you repair that? One of the wires in the loom that you have shown in that above link is for the fuel pressure sensor in the tank - the grey/red wire. While it may be ‘coincidental’, the fact that your 5v reference uses that wire might indicate that your issue with the loom at the fuel tank, and the 5v reference issue, are related....???
 

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Discussion Starter · #19 ·
Thanks for the advice bex. I’ll make time and pull the ecu to get more info and a quick inspection. There’s an electronics repair guy in town I might talk to once I get some info from rhino.

I had the same thought about my taillight wires but the worn loom was after the fuel tank pressure wires separated out of the main loom. I will pull back the shielding though and verify there’s no obvious damage. I have continuity but like I’ve been told, that could be a single strand.

Thanks again for helpful advice. I will report back here WHEN I figure out the solution with links for cross referencing different forums.
 
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