by "DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
Published 12/18/2017 at 22:22
by "DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
Published 12/18/2017 at 22:22
No Tags
STARS: 0
For those not in the know, my coolant sensor (that goes to the ECU) melted in half, so I replaced the connector and sensor. I have continuity across were I crimped the new connector on and I’ve tried two brand new sensors at this point, so I think it’s safe to rule those out. As you could guess the ECU is still not reading the sensor. (Also, I didn’t mix up the wires on the connector and it’s just a thermoresistor so I don’t think it would really matter even if I did.)
Anyhoo. It’s a two pin connector. One wire comes straight from/to the sensor from the ECU. The other does the same but splits off and goes to a few other sensors.
My question is; would this be a good way to trouble shoot it to see if I have a problem upstream of the sensor and it’s connector?
I was thinking, with the sensor and connector connected, checking for continuity across the two wires. To make sure that the connector and sensor are making good contact. The unplugging the connector and sensor, turning the key to accessory (just before crank) and then checking for voltage across the two wires. Since they won’t be making contact with sensor and the ECU should be sending power to measure the resistance in the sensor, I should get a voltage reading (5V is how much the ECU sends through it) if everything is good.
Is my thinking correct or no?
I can draw the wiring diagram if you’d like, but it’s pretty much just what I described and it goes across two pages so pictures would be a PITA.
"AestheticsInMotion" (aestheticsinmotion)
12/18/2017 at 23:16, STARS: 2
Looks like Oppo has abandoned you. Guess that means... I’m your last hope. I can’t actually help you in the slightest, but I CAN give you something that will make your current problem seem small and meaningless.
No facial hair Mario. Enjoy
"MoCamino" (mocamino)
12/18/2017 at 23:19, STARS: 3
I am pretty sure you are right. That sensor is just a resistor whose value changes with temperature. The signal it sends back to the ECU is just the change in voltage drop across it. Checking the voltage at the connector without the sensor plugged in should tell you if the ECU is sending the appropriate voltage.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/18/2017 at 23:23, STARS: 1
Well, at least Oppo has memes. Neither DriveAccord.net or Hondatech have memes!
"AMGtech - now with more recalls!" (amgtech)
12/19/2017 at 00:11, STARS: 1
Have you tried jumping the pins on the connector with the key on? If it makes the needle on the gauge blip, your wiring and ECU are probably good. If that doesn’t do anything, test the wire straight to the ECU, if it’s just a 5v reference this will be easy. It probably isn’t the other wire, otherwise you would likely have issues with other sensors too.
Have you considered the possibility that there is more than one coolant temp sensor? Some cars use one for the gauge, and another for engine management. Maybe you’ve been testing on the wrong one.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 00:23, STARS: 0
Yep, there’s multiple sensors. This one is just for the ECU. It’s a thermoresistor that’s suppose to get 5V. My main question, is with the key one position away from crank, will the ECU send power to the sensor? Because if not then my second test doesn’t really tell me anything. Although I could just do it while the engine’s cranking if that’s the case.
"AMGtech - now with more recalls!" (amgtech)
12/19/2017 at 02:10, STARS: 2
If you mean position 2 or “run” then yeah. Unless you’re looking at it all backwards. If the shared wire is a 5v ref, then the wire to the ECU won’t have anything. Which makes more sense to me. If that’s the case you just need to verify 5v on your shared wire, and continuity to the ECU on the other wire.
"Die-Trying" (die-trying)
12/19/2017 at 08:10, STARS: 1
have you had a chance to check the condition of your grounds? losing ground connections can cause some strange drivability problems. have you tried resetting the computer yet? on some of those little cars, you disconnect the battery cables and touch the cables together for a little bit, and on some others you cycle the key on and off while they are touching. you might check to see how exactly its done on yours....
"RacinBob" (racinbob)
12/19/2017 at 08:25, STARS: 2
From what I see, there is a 5 VDC voltage source and the computer reads the resulting the current across the sensor resistor to ground as a signal. As you do your testing, be careful to not ground your sensor signal as I do not know how robust that circuit is.
So, using a free Harbor Freight volt/ohm meter, I would first turn on the ignition and read the voltage of each wire. One better be at 5 VDC. If neither read 5 vdc, you have a wiring/computer problem.
If both read voltage, you have lost your ground and you need to figure out which wire is the ground wire and ground it, The ground wire needs to read 0 ohms to ground.
Assuming you are good so faqar, chack the sensor resistance before installing it in the head.
You should see somewhere in the range of 3000 to 5000 ohms. If that checks, than you need to solder the sensor plug leads to the harness with your new Harbor Freight soldering kit. Crimp connections do not work well as the signal is very small and a crimp is not reliable. Then clear your codes and see if you still have a sensor fault. Hopefully, that clears it and you are good.
If it clears, go ahead and install the sensor,.
This is the gun that you will buy to get the free HF VOM!
"RacinBob" (racinbob)
12/19/2017 at 08:32, STARS: 2
PS, If you have lost your ground. you need to ground everything back to the computer. It appears BTW, the Black wire is the ground.
"Victorinoo" (victorinoo)
12/19/2017 at 11:42, STARS: 1
To diagnose upstream of the sensor i would do the following: Use the factory workshop manual and find a graph of what the resistances at different temperatures should be. Then find an adjustable resistor (or several resistors of different voltages) at the correct values, and wire them up instead of the coolant sensor. Make sure your key is in the ON/run position (engine can stay off), and then use you OBD2 scanner to see if the ecu is reading the correct temperature. If not, you may have a problem with the ECU circuit that feeds the 5V to the coolant sensor.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 12:32, STARS: 0
I’ve been resetting the CEL correctly. There’s a fuse you can pull and it worked when I fixed all the other CELs it had. I should probably check the ground for the ECU, since I think that’s where the sensor circuit grounds.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 12:33, STARS: 0
So the shared wire will be getting the 5V from the battery? I just kind of assumed it was the ground, but I guess I’ll find out.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 12:36, STARS: 0
Mine’s a little different than your diagram. It’s a green and red wire. One goes straight to the ECU and one splits off to a bunch of other sensors. From what AMG Tech said, the shared one probably gets the 5V from the ECU and the one that goes straight back is probably the ground. So if the ground is bad, I need to check the ground for the ECU itself?
"Die-Trying" (die-trying)
12/19/2017 at 12:41, STARS: 1
yeah, but the battery cable touch method doesnt just reset the cel, it kills out the short term stored memory, and the car gets to relearn a bunch of stuff.....
"AMGtech - now with more recalls!" (amgtech)
12/19/2017 at 12:46, STARS: 0
Not directly from the battery. But look at this this way: shared wire brings 5v ref to sensor, which will lower the voltage based on temperature, then sends this lowered signal voltage to the ECU which it interprets as a temperature. If the ECU sends the 5v, but doesn’t get anything back from the sensor, how does it determine what the temp is?
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 13:04, STARS: 1
Huh, I’ll remember that. Although I don’t think that’s my problem now that I just got back from testing it and
1) the connector and sensor still aren’t making good contact. (No continuity between the two wires on the connector.)
2) the wire that gets voltage either isn’t getting enough (3.5V) or my information that it got 5V was wrong.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 13:07, STARS: 0
Ok so I just tested it.
1) There’s no continuity between the two wires of the connector. So it and the sensor aren’t making good contact.
2) I only got 3.5V from the wire with voltage. So either there’s too much resistance in that circuit or my info that it got 5V was wrong. I also tested it before and after the crimp and it was the same, so I don’t think it’s the crimp that’s causing the lower voltage.
3) I checked for continuity for ground on the other wire. It read 2-3 Ohms. But I used the strut tower as the ground and the wire probably grounds through the ECU on the firewall. So I’m assuming that the few Ohms is coming from the distance between the firewall and the shock tower.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 13:08, STARS: 0
Ok so I just tested it.
1) There’s no continuity between the two wires of the connector. So it and the sensor aren’t making good contact.
2) I only got 3.5V from the wire with voltage. So either there’s too much resistance in that circuit or my info that it got 5V was wrong. I also tested it before and after the crimp and it was the same, so I don’t think it’s the crimp that’s causing the lower voltage.
3) I checked for continuity for ground on the other wire. It read 2-3 Ohms. But I used the strut tower as the ground and the wire probably grounds through the ECU on the firewall. So I’m assuming that the few Ohms is coming from the distance between the firewall and the shock tower.
I’m about to go back out and check the ECU ground just to make sure too.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 13:30, STARS: 0
I don’t have an OBD II scanner, but I checked voltage on the wire that’s suppose to have 5V and it only has 3.5V. So I’ll double check to make sure it is suppose to have 5V and then I guess I’ll have to find what’s causing it to loose voltage? Although it’s worth nothing the battery only has 11V at this point. So maybe that why the wire’s not getting a full 5V?
"AMGtech - now with more recalls!" (amgtech)
12/19/2017 at 14:53, STARS: 0
1) Elaborate please. Did you test from pin 1 to pin 2 of the temp sensor connector with the sensor disconnected? If that’s the case, there shouldn’t be continuity.
2)I don’t know if any systems on any car I’ve ever worked on that use a 3.5v ref, it’s either 5v or 12v, unless we’re talking CAN (which we aren’t). Where does the ref voltage come from? Can you post or link a wiring diagram?
3) Might be ok, I’d focus on the reference voltage first. Are any other sensors throwing faults? Particularly the other ones supplied by this same branch? If they’re not acting up, the ref might not be an issue.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 15:26, STARS: 0
1) I cut away a little piece of the insulation on each wire going to the connector. And tested for continuity across both wires that way. The connector was pushed over the sensor as far as it would go (it did click)
2) The wiring diagram goes over two pages. So do you want me to post both, or just draw a condensed version of it? The wire with voltage goes straight to the ECU. The other one splits off multiple times going other sensors and one path goes back to the ECU (a different pin than the other wire) and another branch goes to ground.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 15:46, STARS: 0
This is basically exact, except the grey wire is white. Yes there’s multiple green and red wires.
I can still upload the actual wiring diagram, but it’ll be more of a mess since it goes over two pages.
Edit: Additional note, the dotted green wire at the top doesn’t connect to the TPS. It just splits off into a whole bunch of other stuff I didn’t track down, and for our purposes, I don’t think is relevant.
"AMGtech - now with more recalls!" (amgtech)
12/19/2017 at 16:00, STARS: 0
There should be continuity through the sensor that way. Might just be an issue with the connector or the sensor. Bad pins in the new connector, mis-pinned connector (like it has three holes for pins but only uses two, and one of them is in the wrong spot), pins crimped onto wires that haven’t been stripped, etc.
Please post actual diagram. Yours is fine, I just want to make sure you’re not missing something that I find to be important, or something like that.
This remote tech help stuff is hard sometimes! Wish I could get my hands on it!
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 16:32, STARS: 1
I got this from AutoZone
I must say, this is much more clear than the one in the Haynes manual. (I couldn’t get a good picture of it for shit.)
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 16:42, STARS: 0
ECT sensor is just below the ECU/PCM in the middle. The wire above the sensor is the red one and the one below it is the green one (It’s kind of hard to see.)
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 17:25, STARS: 0
After some testing and finagling. I was able to get the sensor into the connector and have continuity. Resistance read about 1,000 Ohms. Which according to RacingBobs chart (It’s in the comments to the original post) is too low, it’s about 70 F here.
Also I retested the red wire and it’s still only getting 3.5V. I think I’m gonna try to start it up again just to see what it does.
"AMGtech - now with more recalls!" (amgtech)
12/19/2017 at 17:34, STARS: 0
Not bad. Man I wish they put wire diameters and purposes on there too. Benz diagrams have so much information, it’s great.
"AMGtech - now with more recalls!" (amgtech)
12/19/2017 at 17:37, STARS: 0
Good plan. Based on that diagram, if continuity from the ECU on pin C18 to the sensor is good, and if power supply to the ECU is good, then the ECU is the cause for low voltage. But if you can get it to read after finagling the connection, then you might want to leave well enough alone, assuming it’s relatively accurate.
"AMGtech - now with more recalls!" (amgtech)
12/19/2017 at 17:40, STARS: 0
Is racinbobs chart specific to your vehicle? Or generic? There are lots of different sensors and charts for them, so your reading might actually be ok.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 18:49, STARS: 1
Ah ha! I found it, it’s for a GM truck. I’m trying to get the values for the Accord right now though. Although maybe it’s a common sensor and it’s shared?
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 18:50, STARS: 0
Well the engine’s still not running. So I guess tomorrow I’ll have to check the voltage coming out of the ECU.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 18:54, STARS: 1
I found the chart for my vehicle. It appears to be reading correct (70 degrees and about 1,000 ohms.)
"AMGtech - now with more recalls!" (amgtech)
12/19/2017 at 19:30, STARS: 0
This wouldn’t cause a no-start... Please tell me I’m misinterpreting what you’re saying
"RacinBob" (racinbob)
12/19/2017 at 21:11, STARS: 0
Back in the saddle with my Acura OBD2 Manual. My apology if I provided misinformation earlier.
1. I grabbed a correct chart, you just are reading Centigrade instead of Fahrenheit. Both read about the same for 70 f. But as a point of detail 70 F is about 2700 ohms. If you are reading 1000 ohms, either its about 104 F, or your sensor is bad, or your VOM is bad.
2. The circuit measures voltage drop from the source. The red white wire has a resistor in parallel that bleeds voltage. As such, it will not read 5 volts at the red white terminal. So if it reads 3.5 volts, I guess I am OK with that for the time being as I do not know the voltage of the resistor upstream.
3. Step 1 of diagnosis is to measure continuity to ground. You measured 2 to 3 ohms which compared to 1000 ohms between the green/black wire and ground so I think you have a good ground. I think this passes.
4. Assuming you find a good sensor that plugged in has a solid 2700 ohms across it, I would solder it up (do not crimp!). At this point, I would install it and see if with a scanner if the code clears. If not and you get PO117 or PO118 I will send page shots later. My bet this will fix it though
"Victorinoo" (victorinoo)
12/19/2017 at 21:47, STARS: 0
If it’s reading 3.5V, you may have a short somewhere in the wire. Check another 5V reference circuit and compare. It’s possible that the battery benign low may cause it
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/19/2017 at 22:13, STARS: 0
The problem is that AMGTech and trail of blown headgaskets are saying it the other one that should have a voltage reading, the wire with 3.5V shouldn’t have any voltage (with the sensor disconnected.)
Also I did check the battery, its still at 12V.
"RacinBob" (racinbob)
12/19/2017 at 23:22, STARS: 1
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/20/2017 at 00:28, STARS: 0
Awesome, I’ll see if I can check out a scan tool from AutoZone or O’Reilly’s tomorrow.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/20/2017 at 14:12, STARS: 0
Are the ECU and ECM the same thing or different? because I pulled up the carpet in the passenger side, and there’s two very ECU looking things, one’s dead center beneath the radio and the other is closer to the passenger side and the firewall. The second one looks like it has the connectors I’m suppose to test though, with the four different connectors.
"RacinBob" (racinbob)
12/20/2017 at 18:17, STARS: 1
Here’s what they say for a 2000 Accord. Its on the right. http://www.fixya.com/cars/t1666298-still_find_ecu
I would say though that it appears to me that the wiring is fine because you are seeing voltage on one wire and a ground on the other. The ECU is also pretty reliable so I wouldn’t put much effort into checking it until you have nothing left to check.
Remember, we are having this problem due to a failed temp sensor. Let’s get a correct one installed and clear the diagnostics and see if it works. I bet that the wiring and ECU (Engine Control Unit) have always been and are still are fine.
BTW I would not minimize the need to solder the connection. Honda makes a point about intermittent connections causing faults. Computers are fast and even a 10th of a second is enough time to fault one.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/20/2017 at 18:23, STARS: 0
Guess I’ll see what happens when I put the OEM sensor in. Although I still think there’s gotta be something wrong with the wiring since it’s only getting 3.5V, not 5V.
"RacinBob" (racinbob)
12/20/2017 at 20:23, STARS: 1
Folks there are many ways for sensors to work as shown by my Honda OBD2 schematic.
1. One way is for the design to have a source voltage and read the voltage coming back.
2. Another way is provide a regulated voltage source (marked 5 V )
and then to put a known resistor downstream (highlighted yellow ) and have a circuit read the voltage between resistor (Marked VS ) so you can calculate the resistance the sensor you want to read. This is the version of circuit used by Honda.
There is a very smart reason to pick option 2. If there is a short circuit, the upstream resistor limits the current protecting the DC power supply and allowing the other sensors to continue to work.
Not bad huh. That’s how I think most car sensor are designed.
Where am I going with all of this? Well the highlighted resistor has a voltage drop so it is no surprise to me that there be 1.5 volts across it. I can always be wrong, so that’s ok, however the schematic clearly shows a resistor upstream so I feel pretty good that what ever the circuit, the downstream voltage would not surprise me to be less than 5. In fact it almost has to be less than 5.
"DC3 LS, will be perpetually replacing cars until the end of time" (dc3ls-)
12/20/2017 at 20:28, STARS: 0
The only thing though, is that I think that diagram is only for the V6 models. My car (and someone else said all the 4cyl are like this) doesn’t have the “D” connector on the ECU, it goes through the “C” connector and none of the wiring diagrams have shown a resistor, although you could still be right.
"RacinBob" (racinbob)
12/20/2017 at 20:47, STARS: 1
Honda uses the same sensor design on for OBD2. In fact I bet it’s the same sensor, civic or NSX..... Most schematics don’t show the resistor, in fact the other schematic in my manual doesn’t show it and in fact till I noticed it, I had no idea that it was this design. I too assumed 0 to 5 back like others.