Great diag and explanation. So sorry about the paper clip! No matter what type of tool it is, a person does get attached to them! I hope the new one eventually gets the same feel and comfort as the old one. (Maybe it might even turn up! We can only hope!) Thanks for posting.
@@SchrodingersBox I actually do! We all have our favourite tools, and the replacement, no matter what type of tool can either be better, or many times, worst. Enjoying your content and your process of diagnosis. Keep up the great work and your kindness in sharing.
I am new to your channel, but I want to say THANK YOU for talking out your internal thoughts and explaining everything very thoroughly. As someone trying to learn, that is super helpful. With some other videos, they will often just hit the highlights, but not explain every step and more importantly WHY. Anyhow, thanks again and I look forward to more videos.
Hey and first of all thanks for another great diagnostics video. I was struggling long time with this 5v ref voltage / signal return idea. You once again, told it as we say in Finland "beer&sausage" model instead of making it difficult to understand. Now it makes sense and i know how it works.
I have a simple, old kitchen knife that I’ve had in my toolbox since the rocks were cooling. Lost it for a year or so but thankfully it’s found its way back home again. Hope your paperclip turns up again for you.
I pray every day for the return of my paper clip. What’s funny is one day last year when I noticed that Borla hat I have worn in almost every single video for 8 years went missing . I’ve had it forever and couldn’t find it to save my life so I got a new one. Months later- like maybe 6 months a repeat customer came in to get brakes done. While working on the brakes I saw my hat tucked in between the engine and firewall. I was so relieved!!!! Miracles happen!!
Love the sarcasm, you keep saying TWO coolant temp sensors. One is a sender and it uses a 10 volt pull down signal. Great video, credit for working on older cars.
I'm so sorry about the loss of your special paperclip. It's obvious it meant a lot to you. I was at Warren and Annabel's Magic show in Maui (before it burned to the ground), and one of the magicians was crushed when he handed a can of spam to a person in the audience, and that person opened it and ate some. The magician said that he'd had that can for 9 years, and never had an attendee do that. On the other hand, however, it tells you that 9 yr old spam is still quite edible. o^O
96 Jeep Grand Cherokee 5.2L V8 uses the shared 5VDC reference signal. Yep, if one shorts you do have a No Start situation. Ask me how I know. :) Great video, as usual. Thanks.
I have the maxisys906bt, I am going to buy the smoke machine you mentioned in another video that had its own battery. I want to get a pico pressure transducer, could you tell me the exact setup you have for performing tests as in what pico scope etc.. Do you have a list of all your diagnostic tools or recommendations? In another video I saw an inspection camera hooked up to your phone, things like that
Hey Matt, I always learn a lot from you but at this time I’m seeking for a piece of advice. I’m working on a Honda CRV. I’ve replaced most of the coolant pipes that were eaten by rats. Finally got the car to start n it had no leaks. While the car was idling, i could hear it misfiring and vibrating and i find the check light flashing. I hooked up my mini Launch scan tool and i did get a P0303 misfire code. I cleared the code as I always do, just to reproduce the symptom. Eventually it came back on. I went to check for power, ground and signal on the coil pack plug, all was there. I swapped cylinder no*4 coil pack n s.plug with cylinder no*3. Still was getting the same code. I went on again and checked for power on the no*3 injector plug and it was there(also checked on the rest of the injector plugs). Swapped again injector no*3 with no*4,still was getting the same code. So while the car was idling, having injector no*3 unplugged checking for that open n close ground from the PCM( there was constant ground only on injector plug no*3). Left the car because it had a clutch problem since I’m not a mechanic, will have to go back to the car cause I’m not done yet. I got to think that it might be the problem within the PCM. Got me thinking again that that signal wire could have a short to ground, which I’m going to check once I get back to work on that car. LOL i know my story is long, but will you just help me out because there might be something small that I’m missing. Reply me when you come back from your trip. Thank you 👍🏾. All the way from Zimbabwe 🇿🇼.
@@SchrodingersBox Excellent follow-up question Matt. I don't know what year this CR-V is, but if this is a 1st Gen (1996-2001), those engines were prone to valve burning problems due to a lack of proper valve adjustment. The recommended 30k mile (48000 km) valve adjustment (which is very easy to do) almost never gets done. I'd try a valve adjustment first. Sometimes there's not enough "adjustment" to get the gap correct. Then, if the compression test also fails, the head needs to come off because the valve is burnt too badly. Sometimes you can get lucky and just get by with a valve adjustment only. I've been down both paths with 4 different CR-V's. If this is a newer CR-V, it's likely none of this applies 🙂
Nice video. The diagram that you draw at around the 19:00 mark I believe may be wrong. According to Paul Danner, a Thermistor's 5 volt reference is never shared with other inputs. The ground circuit can be shared though. I'm referencing chapter 6 of his book on page 6-2.
@@SchrodingersBoxInteresting. It may not be the norm though. I might try to contact Paul and see if he has seen that since writing his book and teaching that in his classes over the years.
@@SchrodingersBox Paul responded to me and sent me a RU-vid video link to watch for a better understanding of the thermistor vs a Potentiometer in relation to the 5 volt reference. Here is the name of the video. "Thermistor-Potentiometer comparison and the 5v reference circuit". From watching the video, I got that the 5 volt reference is shared internally in the PCM for both types but externally they do not share it due to the resister in the Thermistor circuit.
Unfortunately you are incorrect in your description/drawing of how the PCM monitors voltage here - it is, in fact, looking at the voltage drop across the ECT (or IAT) sensor and not the internal resistor. When the engine is cold it will read a higher voltage bc the resistance of that NTC thermistor is large at that point, but as it warms up the resistance will decrease and the voltage reading will also decrease accordingly.
It does read the internal resistance voltage- NOT the sensor voltage. The sensor voltage will always be a full voltage drop to zero no matter what the resistance is. You are correct in that the NTC resistance is variable however it does not read voltage drop across the sensor itself. It is impossible to do that. At best some designs may compare downstream of the internal resistor and compare that variable voltage to ground… but it definitely can’t read voltage drop across the sensor. If it did that there would have to be more than two wires at the sensor to measure the voltage on it.
@@SchrodingersBox If I'm wrong, and you're right, then as the coolant temperature rises it should do the opposite of what I said i.e the voltage reading should increase as the temperature increases (bc the internal resistor becomes proportionately "larger" in the circuit as the resistance of the ECT sensor decreases, and therefore shows an increasingly larger voltage drop across said internal resistor). Correct? You've got a scan tool there that shows both the calculated temperature from the ECT sensor and the voltage the PCM is seeing - go ahead and do a cold start and watch those values as the engine warms up and see what happens.
No- voltage reading absolutely decreases with temperature increase. we saw that when I shorted the circuit out - removing all resistance as opposed to infinite resistance which showed 4.6V. shorting it showed 0V. installing the new sensor showed about 3V at 65 degrees. This is because as the thermistor warms up it reduces resistance proportionately. what we are seeing in this system is the voltage drop across the INTERNAL resistor compared to ground. As a matter of fact there are often wiring diagrams that actually show the internal “DVOM” connections inside PCM measuring at the internal resistor. It literally shows this. As the variable resistor heats up, its resistance decreases which means voltage decreases- but again- if not for the internal resistor in the PCM we would not see this. the voltage before the variable resistor would ALWAYS be 5V and the voltage after the variable resistor IS ALWAYS 0V. the internal resistor voltage drop is what causes the varying voltage between the fixed and variable resistors. THAT is what is being measured- the the voltage drop across the variable resistor. this is why we see the voltage lower and lower as the variable resistor warms up.
@@SchrodingersBox "THAT is what is being measured- the the voltage drop across the variable resistor." - now you've got it 😉 Unless that was just a Freudian slip, in which case we're back to square one. It sounds like you're erroneously conflating the need for a pull up resistor in an ECT circuit with what is actually being measured in said circuit. If you look at a wiring diagram for ANY 2-wire ECT sensor you'll see that the voltage reading is taken AFTER the internal resistor but BEFORE the ECT sensor and referenced to GROUND. This is what you did when you backprobed the wire coming out of the PCM - did you attach the other lead on your multimeter to the 5V source before the internal resistor, or did you attach it to ground? We both know you attached it to ground, and that is the voltage drop across the ECT sensor, and that's the same thing the PCM does internally. I keep wondering if this is just some sort of communication snafu but no, you said the PCM is looking at the voltage drop across the internal resistor and even drew a picture demonstrating as much, and that is 100% incorrect.
There is one problem. The PCM first design is NOT measuring across the resistor ( pullup resistor design) . The PCM for that Coolant sensor is measuring on the negative side of the resistor with respect to ground. The internal DVOM is measuring with respect to ground. When the CTS is unplugged , it is the same as an open sensor. The scan data will read HIGH, a full 5 volts. If the internal DVOM measured across the internal resistor there would be ZERO voltage drop , because there is no current flow. The easiest way to determine if a circuit is a pullup or a pull down design, (your first example or your 2nd example), is to measure what happens when the sensor is totally disconnected. In example 1 , with the sensor disconnected, the resistance is infinity, far in excess of the minus 40 degF temp. With the resistor in the power side of the circuit, and the measurement point internal, the voltage measured goes to 5v HIGH, this means it is PULLUP to a logic HIGH. The opposite happens in your example 2. When the CTS is disconnected in example 2 the PCM measures ZERO volts , the logic LOW , a PULLDOWN circuit, and because it measures on one side of the resistor it is protected from " floating " to either high or low which could happen when wires are near high voltage and current wires. I believe you understand but it is not coming out in words. It is important to NEVER use a conventional test light to check for the 5volt pullup design.. This is because the internal pullup resistor might be about 5 KOHMS , and the test light only has less than 50 ohms of resistance. There is not enough voltage available to light the test light because 99% of the drop occurs thru the pullup resistor. When a 10 Mohm DVOM is used, you can then measure actual 5 volts because there is only a small drop across the 5K ohm resistor ,as compared to the 10M ohm in the DVOM. Do the math , I did.
If you look thru the comments you'll see I pointed this out yesterday, but he doubled down on his initial assertion that the PCM is measuring across the pull up resistor 🤷♂️ Hopefully he gets it eventually and offers a correction bc you can see from all the additional comments in that thread that it's leading to a lot of confusion/misunderstanding.
Hi Matt, I try what you do. Problem is am south African. I tried Mitchell DIY , it wants American address. But eventually they did what they did and I subscribed. I looked for wiring diagram for Ford ranger t6 wild track. Is not there. When I ask why since Ford is American car. They said cars produced out of America they don't cover. So where can I find wiring diagram that covers both American and European. Your follower South Africa
Wow man not sure I can help with that. I didn’t know they require American address. I once in a long while also have had issues finding diagrams for some unusual vehicle. I was trying to find one for an old ford box-truck like a delivery vehicle and there wasn’t one for the specific model.
the purpose of the internal resistors in the pcm is to CONVERT sensor CURRENTs to voltages. The two-wire sensor is a current throttle wheras the three-wire is a voltage throttle. The common ground is irrelevant as it is ONLY ground.
given a variable resistor.. then it reports its measured 'position/condition' as changing R. The current through it yields a varying voltage => V = I × R. Most generally speaking a fixed voltage is applied and the result is a varying current. You are correct in that there's a secondary, fixed resistor in series that forms a voltage divider. And it's the voltage across this FIXED resistor that is the marker of the sensor's position, NOT THE VOLTAGE ACROSS THE SENSOR. i.E., the resulting voltage across the sensor can be confusing because if the sensor's R goes down its I goes up...Possibly the sensor's voltage mighr STAY THE SAME. The 2wire experiences CURRENT changes while the 3wire does NOT. The 3wire ouputs variable voltages; the 2wire yields variable current.
resistor (fixed one internal to PCM) yields voltage in proportion to its current. As sensor R decreases the fixed R experiences increased I and also increased V.
What?!?!? The dedicated sensor wire IS the ground. That’s two wires. What’s the third wire? It’s a thermistor. Not a Hall effect. What is the third wire going to be for on a thermistor?
Hi my name is Damion, I'm fairly new to watching your channel. I'm gonna cut to the chase. I have a 02 chevy avalanche z71 that's experiencing a crank no spark condition. I've replaced the fuel pump, starter, crank and cam sensor and it still won't start. Prior I removed the clutch fan and installed duel fans that I have to turn on manually. Reason I'm telling you is because 1 night I fell asleep in my truck while it was running and forgot to turn on my fans and when I awoke the truck was off and it smelled like a faint burnt oil smell in the cabin. The truck would not start from that point on. I've thru parts in attempt to get it to start up to no avail. I've been watching your channel and you seem to be more knowledgeable on these issues. Please if you can help me diagnose the problem ... thank you
C R A P .. follow on response to this was an exvellent observation that the meter read "OL" NOT 0 ohms as was reported. Part 1: You measured 5V at firewall and the P0018 says failed high= open. Yet you measure sensor = 0 ohms and claim it is failed. You short the sensor connector (0 ohms again) and it responds on scan at +253 °... Yet the initial failed reading was -40° with circuit as originally discovered?? This might suggest a loose connector pin resulting in an open circuit This is Why the shorted sensor doesn't read at firewall but, instead, = 4.7V. /// and the observation below explains it all: When measuring the sensor the DVM yielded "OL" NOT 0 ohms.
The failed sensor was open inside, it is infinate resistance, not zero. The meter is actually reading out of range. Same value if the sensor was unplugged. The voltage will be HIGH a full 5 volts at the point of measurement internally in PCM because there is no current. So with respect to ground there is 5 volts on both sides of the resistor. When the wire connector is shorted to ground there is almost zero resistance, the current flow at the maximum amount ,and the 5 volts will drop across the resistor to zero volts, which will register as " voltage LOW.
