Alternator AC Ripple - Page 1
Forum section: electronics / beginners

author: Alias2
author_rank: Newbie
timestamp: October 07, 2023, 10:12:16 pm
content: Hello All,Recently got my first oscilloscope to test the alternator on my 2008 pathfinder. I'm getting a cam shaft sensor wiring error code but I changed both camshaft sensors sensor a few months ago with a dealer parts and so I'm a little suspicious of my alternator. Comparing the scans I'm getting to the info I'm looking at online isn't giving me a clear picture. Things seem noisy. I think it's because I'm connecting to the battery clamps and to the car body and not directly to the alternator. The location of the alternator isn't really accessible.If anyone can give me some input on the below pictures and if they look good or not, I would appreciate it.Code is P0340 "AP0340 error code indicates a problem with the Camshaft Position Sensor A circuit. It's possible that the wires leading to the camshaft position sensor are faulty, or that the sensor itself has failed. This error code isn't a sign of bad camshaft timing."Pic 1-2 are at idle and 3-7 at 2krpm

author: Benta
author_rank: Super Contributor
timestamp: October 07, 2023, 10:24:30 pm
content: Look perfectly normal to me.BTW, this is not an "auto-repair" site.

author: DimitriP
author_rank: Super Contributor
timestamp: October 07, 2023, 10:27:25 pm
content: Since you went through the trouble of 'scoping things around, did you check the knock sensor input to the ECM?DC vehicle power is never "clean" , unless the engine is not running

author: DimitriP
author_rank: Super Contributor
timestamp: October 07, 2023, 10:29:18 pm
content: Quote from: Benta on October 07, 2023, 10:24:30 pmor toaster, refrigerator or washing machine, but what are you trying to say ?

author: Alias2
author_rank: Newbie
timestamp: October 07, 2023, 10:32:38 pm
content: Quote from: DimitriP on October 07, 2023, 10:27:25 pmNo I haven't made it that far.Will give it a look though once I find where everything is located.

author: Alias2
author_rank: Newbie
timestamp: October 07, 2023, 10:39:35 pm
content: Quote from: Benta on October 07, 2023, 10:24:30 pmWhen I look at the 1st picture on the site below for what a correct alternator at 2krpms look like and compare it to say picture 3 or 4 that I posted, I think there are a lot of spikes and dips. But none of my pictures really match any of the examples for bad alternators on that site.https://autoedu.info/en/auto-electric/alternator/oscilloscope-alternator-test/Has me a little perplexed.

author: bdunham7
author_rank: Super Contributor
timestamp: October 07, 2023, 10:45:22 pm
content: That doesn't look broken to me. You need to be clear about exactly which knock sensor code you have--there are different problems with the knock sensor that can be reported--failure to show a signal when one expected vs signal when not expected, for example. Is your engine quiet?

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 07, 2023, 10:45:53 pm
content: The battery acts as filtering element for the ripple, just like a giant capacitor.As they age their filtering capabilities get worse, when really bad it's common to hear this ripple as a whining sound when increasing the volume of the radio, a "Whiiiiirrll" just like a bad bearing.However I can't tell if that ripple is ok or not, all I can only tell, 4-5 years ago I started to hear this whine when playing music, the battery died shortly after!A new battery restored the Hi-Fi sound

author: Alias2
author_rank: Newbie
timestamp: October 07, 2023, 10:57:04 pm
content: Quote from: bdunham7 on October 07, 2023, 10:45:22 pmThe engine sounds smooth. I don't think there is a knock problem.The code is P0340."A P0340 error code indicates a problem with the Camshaft Position Sensor A circuit. It's possible that the wires leading to the camshaft position sensor are faulty, or that the sensor itself has failed. This error code isn't a sign of bad camshaft timing."

author: bdunham7
author_rank: Super Contributor
timestamp: October 07, 2023, 11:01:09 pm
content: CMP sensor ≠ knock sensor?

author: Alias2
author_rank: Newbie
timestamp: October 07, 2023, 11:02:47 pm
content: Quote from: DavidAlfa on October 07, 2023, 10:45:53 pmI have heard that before sound over a radio on older cars but not on this car. Good to know. The battery was replaced about a month ago. The previous one was about 4 years old so nothing out of the ordinary there I would think.

author: Alias2
author_rank: Newbie
timestamp: October 07, 2023, 11:04:35 pm
content: Quote from: bdunham7 on October 07, 2023, 11:01:09 pmYou are 100% right. I don't know why I always call the cam shaft position sensor a knock sensor. I've corrected my original post.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 07, 2023, 11:08:26 pm
content: "This error code isn't a sign of bad camshaft timing".I could be a timing issue. I know nothing about you engine, but had exactly this about 10 year ago on a different car, replaced the sensor, no way.Few weeks after it started to develop a slight tickign sound. Next week it became a rod knock!The crankshaft sprocket has a locking/alignment key to fix it into the crank so it could only coudl be installed in one position, but it had broken and slighly shifted from the timing position.So indeed the valves were "kissing" the pistons!. Luckly the engine was fine, only required a new sprocket.

author: Alias2
author_rank: Newbie
timestamp: October 07, 2023, 11:33:10 pm
content: Quote from: DavidAlfa on October 07, 2023, 11:08:26 pmHopefully that isn't the case. I guess Monday I'll swap out the one cam sensor and see how things go. Does make me wonder if the cam is floating a little.

author: bdunham7
author_rank: Super Contributor
timestamp: October 08, 2023, 12:12:31 am
content: Quote from: Alias2 on October 07, 2023, 11:33:10 pmAre there not 2 CMP sensors? IIRC, there are and the P0340 refers to one of them, the other has its own code. Again, IIRC, I believe mechanical issues can cause this code, from the variable cam timing phasor to valve adjustment. Your scope can be connected so you can have a look, but hopefully you have two channels so you can look at the crank sensor (CKP) at the same time.

author: Alias2
author_rank: Newbie
timestamp: October 08, 2023, 01:53:24 am
content: Quote from: bdunham7 on October 08, 2023, 12:12:31 amThere are 2, the driver side and passenger have their own code. About 6 months ago maybe more I had a code pop up and replaced both. It is why I'm leaning a little towards a signal or wiring issue. So far while researching this code I haven't came by any timing issues as being the problem. But I'm not ruling it out. Some say the crank sensor could be a problem too. I just hate throwing money at a problem and not knowing what it is.

author: G-son
author_rank: Regular Contributor
timestamp: October 08, 2023, 10:05:47 am
content: Have you scoped the sensor signal, power feed and ground? As that's where the code is, checking what the computer actually sees to set the code may help.

author: CaptDon
author_rank: Super Contributor
timestamp: October 08, 2023, 02:05:36 pm
content: If it is a potential wiring issue then perhaps unplugging and re-plugging every connection in line with that sensor may help including the connection at the E.C.U., you must however disconnect the battery cable before fooling around with the E.C.U. itself!! Is this a 'timing belt' car?? If so belt stretch will cause exactly this error code. Also, if the engine ever spun backwards from dieseling (not likely with fuel injection) the tensioner (belt or chain in this case) will not have arrested the slack properly and the cam associated with that sensor may have jumped one tooth. Had that happen on a Hyundai B.T.W.

author: G-son
author_rank: Regular Contributor
timestamp: October 08, 2023, 05:01:37 pm
content: Unplugging and plugging back in may get rid of thesymptomfor now, but it's likely to come back sooner or later - the problem is still there, you just scraped some oxide off the contacts so it works for a while. I'd much rather spend a bit more time trying to narrow downexactlywhere the problem is so I know what to spend work on fixing.Are you sure about getting P0340 code for a stretched belt? It's a circuit error code (no signal), not a cam timing code. There are plenty of different codes, sometimes you get the wrong one, sometimes a correct one, that's why it's such a good idea to hook up a scope and verify what's really happening. If you find a known good cam/crank correlation waveform you can check if the timing is good or not.

author: alligatorblues
author_rank: Regular Contributor
timestamp: October 08, 2023, 11:40:54 pm
content: Quote from: G-son on October 08, 2023, 05:01:37 pmWith a CAN bus to serial adapter you can connect the car to a laptop. That will give you a hell of a lot more information than guessing where to connect a scope.

author: G-son
author_rank: Regular Contributor
timestamp: October 09, 2023, 06:38:53 am
content: Quote from: alligatorblues on October 08, 2023, 11:40:54 pmThe onboard diagnostic feature in cars can be a VERY powerful tool when it comes to finding a problem. The issue with it is that you are basically asking a defective computer to tell you what the defect is, and on top of that it's limited to just "understanding" what it has been programmed to understand - and that's still assuming that the defective part isn't confusing it, making it interpret one problem as another.So, absolutely, using the built in diagnostic feature is great to figure out in what area the problem most likely is. But once you have that code for, like in this case, a missing signal from a sensor, you need to figure out if that's a dead sensor, no power feed to the sensor, no ground to the sensor, a broken or shorted wire from the sensor, or a broken computer receiving a good signal but not understanding it. Or you could simply fire the parts cannon, i.e. throw new parts more or less related to the fault code at it until the code disappears - or give up when you've spent more money than you like on not fixing anything, and leave the car to someone able to actually find where the problem is.

author: DBecker
author_rank: Frequent Contributor
timestamp: October 09, 2023, 04:18:32 pm
content: A bit of general background on automotive sensors that might help to track down the problem.Automotive sensors are usually powered by 5V. The ECU has multiple 5V tracking supplies so that a fault doesn't shut down all of them, and so that plausibility checks can be done (e.g. pedal position). They are 'tracking' supplies, a copy of the master 5V reference, so that ratiometric sensors on different supplies report the same values. This is especially important during cranking, when the battery can sag below the drop-out voltage.The 5V supplies are monitored for at least a short to ground, often a short to 12V, and sometimes for current draw in the proper range. If only a single sensor is on the supply, that sensor is "blamed" for any voltage or current fault.Similarly the sensor output is tested for good continuity and monitored for plausibility. Old ECUs would use a simple scheme, such as a high value pull-down resistor. Modern chips can switch in a weak pull-up or pull-down current. This can detect a sensor or connector problem that a VOM on the output won't catch.