noise."Mechanic: Learning from Failure · 3:40am Sep 25th, 2021
Alrighty, kids, time for another mechanic blog post, yay! Y’all know the drill.
Source
Eh, close enough
Today we’re gonna look at a Dodge Avenger!
Came in on a hook. It’ll crank over just fine, but it won’t run at all.
My manager opened the hood and poked at it while I was doing something else, and then it suddenly became my baby.
Sure enough, it would crank over but not even try to fire. Also, the electric throttle body light was flashing. On drive-by-wire cars, they’re pretty obsessive about making sure the car doesn’t run away, and malfunctions may limit the amount the throttle can open, or may even cause it to stop injecting fuel (which is a good way to make sure the car doesn’t accelerate off when you don’t want it to). It could be that the car won’t start because whatever throttle malfunction it has is causing it to not inject fuel.
So I grabbed the scan tool and the first thing I did was pull codes:
P0456 Evaporative Emissions System—small leak
P0440 Evaporative Emissions System—general failure
U0402 Implausible data from Transmission Control Module
P0369 Camshaft Position Sensor (CMP) Intermittent Bank 1 Sensor 2
P0335 Crankshaft Position Sensor (CKP) Circuit
P0642 Sensor Reference Voltage 1 (VREF1) low
P2122 Accelerator Pedal Position Sensor 1 (APP1) circuit low
Since I was there, I took a look at a couple bits of data. APP1 never changed voltage (it should have read between .5V and 4.5V, depending on how much the accelerator pedal was pushed). Chrysler tells you if the CMP and CKP are synced (they should be); on this car they weren’t. Mind you, not having one signal means no sync, it doesn’t mean it’s out of time.
I also looked at the injector pulse width command, and it was not commanding any fuel. Which would explain why it doesn’t even try to start, and is intentional.
Now, it’s rare that you’ll have multiple simultaneous system failures, so we’re gonna start by seeing what everything has in common. Cast your minds back to the 2015 Escape with the VREF failure. That only had one code for an APP sensor.
This Chrysler’s got lots of codes.
And in fact, from some quick Identifixing of the P0642 code, I found out that the CMP, CKP, and APP1 are all on VREF1, so anything wrong with that circuit will set all those codes.
At the moment, I don’t have a bay I can pull the car into, I’m working out in the parking lot. What I have figured out, though, is that I can watch the APP1 on the scan tool, which is currently showing .15V (remember, it should be at least .5V) If I unplug every sensor I can get to under the hood which might be on the VREF1 circuit and the voltage gets normal, then I’ve found the problem.
If you don’t remember the Escape and didn’t click through to the link, it had multiple 5V outputs from the PCM, but internally several of them were connected (which makes sense in hindsight) and so while I thought I’d ruled everything out and it had to be a PCM, it wasn’t.
The Chrysler wiring diagram shows five different 5V outputs, but I don’t know how it’s arranged internally. I do know that there are at least two separate 5V output circuits (VREF1 and VREF2), since both the APP and Throttle Body will use two different 5V supplies so that one failure won’t make the car do something unexpected.
Also, the wiring diagram shows that APP1 has a different 5V source than the CKP and CMP, although Identifix suggests they’ve got the same source.
Casting our minds back to the Escape, what I ultimately found was an EVAP sensor under the car that had mouse-chewed wires and which was on the same VREF as the APP.
And those of you who haven’t had the whole can of beans yet have probably noticed that this Chrysler has not one but two EVAP codes. I sure noticed that.
I also know that the little component which monitors EVAP leaks on this thing is known to get water in it and corrode up into the connector, which could cause a short circuit and take down VREF.
So when I get the car in and lift it up, the first thing I go for is the ESIM* (that’s what it’s called), and it’s filled with corrosion. I get it unplugged, make sure the two terminals aren’t making contact, and look over at the scan tool wondering if I’ve knocked this one over the fence.
Nope.
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*Since Chrysler is always changing their acronyms, it could be an ESIM, a NVLD, or a LDP, but it does the same thing no matter what they call it
Well, that’s okay. Now that I’ve got the car up in the air, I can get to the CKP. That’s on the back of the engine, just above the right driveshaft, protected by a heat shield held in place with an unnecessary number of bolts. Which are also two different sizes. Thanks, Chrysler.
Unplugging that does fix the car. The APP1 goes to .8V, so I lower the car back down and sweep the throttle, and now APP1 responds.
The car won’t be happy to start without its CKP, but it might . . . for good engine control, you need both CMP and CKP, but for just running, you usually only need one of them.
And indeed, after a longer than normal crank time, the car fires up. The electronic throttle body warning light isn’t flashing any more, and the car seems to run fine.
A lot of these blog posts, now comes the twist. But in this case, there was no twist. The CKP had shorted internally, and it took down everything on that 5V circuit.
The ESIM wasn’t on that circuit, that was a separate entirely predictable failure on this car. If I had to guess, the check engine light had been on for a while and the customer didn’t care until the car wouldn’t start.
Ugh, the Tesla truck is fugly.
Seems to be more of an electrical blog rather than mechanical.
I’m going to have to use that specific term when throwing an exception instead of the dull “out of range” verbiage.
Well the thing about modern CKP / CMP sensors is that they are digital. The three wire ones. Meaning they are basically a tiny computer circuit board in there, along with a traditional hall effect sensor. And like most electronics, they don't like being baked.
Hmm. Implausible but not impossible. What kind of data could you possibly get that is unexpected but still possible. Its a transmission.
Woah, lots of gibberish in this one. At least there's cute ponies!
The photo of the Izzy plush and all the cans of beans is probably my favourite!
5586682
But it does look like what people in decades past thought today's vehicles would look like.
""Y’all know the drill."
[shows picture of Izzy and her horn...chisel?]
"Eh, close enough""
:D
...I am not sure that that unicorn is using a very safe tower-climbing procedure...
Thanks for the mechanic-talk and pony-pics. :)
5586682
It looks like a doorstop crossed with a DeLorean.
I can’t help but wonder if it’s a look that’ll grow on people, though. I dislike the shape less than when I first saw pictures of it.
5586705
Be honest, that’s how lots of these blog posts are. Electrical diagnosis is more blogworthy, usually.
You should, although it’s technically an ‘out of range,’ code, more of an ‘out of expected range for current operating conditions.’ I’ll cover that more in the next mechanic blog post, actually, ‘cause I just got a Ford that had an ‘implausible’ code (although Ford doesn’t call it that).
5586783
If this one died of being baked, than the heat shield (and its unnecessary quantity of bolts) didn’t do its job.
I will give them credit, though, the sensor itself came out a lot better than the ones in cast iron blocks usually do.
5586796
Usually what they mean by that is that the reading is a possible reading, but it doesn’t make sense with current operating conditions. One example with a transmission is that it might report it’s in multiple gears—it can be in any of them, but it can’t be in two of them at the same time. Or the input speed sensor on the transmission showing that the input shaft is turning faster than the engine while the car’s in park and the torque convertor is unlocked (as it would be in park). That could also indicate a problem with a different system, say the output shaft is turning near its maximum speed but according to the ABS none of the wheels are moving, it would probably assume that one transmission sensor had a problem rather than four individual wheel speed sensors.
Sometimes (and we’ll get to this in the next mechanic blog post) different sensor values on the car are compared, like various temperature sensors when the car has been sitting for a while. All their values should be close; if they aren’t, even if one of the sensors is reporting a temperature that’s within its normal operating range, it’s unlikely to be a valid reading.
The one I’ll be blogging about next is a Ford, and they call it a range/performance code (although that’s referring to a specific sensor, rather than module communications).
5586844
That’s always the saving grace, even if the mechanic stuff is pure gibbrish, at least there are cute ponies.
That one is adorable. And I dunno if you noticed, but those appear to be Dutch beans.
5587016
I thought they’d look more like this:
upload.wikimedia.org/wikipedia/commons/thumb/6/63/1996-2000_Toyota_Tarago_%28TCR10R%29_GLi_van_02.jpg/1920px-1996-2000_Toyota_Tarago_%28TCR10R%29_GLi_van_02.jpg
I don’t know if it’s better or worse that they don’t.
5587905
Probably not, although maybe they’re using the show-accurate hope that if they fall, a pegasus will catch them before they hit the ground.
You’re welcome!
5588909
Hah, maybe. :D
:)
5588897
I still don't like it: practicality was completely dropped. I couldn't move much hay with that because of the bed design. A classic 8-ft bed can haul 59 regular square bales without breaking the legal height limit. You'd be lucky to haul more than 12 on that glorified California science project.
5589346
To be fair, a lot of the trucks are sold to people who don’t need them for their bed capacity (or in many cases don’t need them at all), so Tesla might have felt that it was better to make a bold statement rather than a truck that’s useful for all.
At the same time, I’m with you; I’d rather have a longbox that I can fit whatever I want in. Kinda bummed that my Dodge is a shortbox, but then at the price I was willing to pay when I bought it, I didn’t have a lot of options.