# Check Engine Light P0502



## nuclearsteel (Jan 12, 2014)

So while driving this morning I got a CEL that popped up. The online issue I noticed is that the engine seems to stop pulling power at about 4500 RPMs. Felt like it hit a rev limiter. I drove it to work (about 45 miles) and checked the CEL. 
Got a code P0502 Vechile Speed Sensor A Circuit "Low Input" Confirmed. 

So I reset the light and when I started driving the speedometer was at zero even though I was moving...this went on for about a mile that the speed came back. No CEL yet, but given the no speedometer reading for 1 mile...something isn't rigiht. 

The car is a 2014 1.4T with a MANUAL transmission. I suspect a speed sensor in the transmission or the associated wiring (provided there is one for a manual transmission...seems there almost has to be) Thoughts?

Also, seems if this is the problem and the wiring is fine (not cut or chewed) and it is the sensor this should be covered by the 100K mile power train warranty?


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## obermd (Mar 3, 2012)

When it returns, don't clear the CEL. Instead take it in to your dealership. I suspect you're correct but your car is under the B2B warranty.


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## nuclearsteel (Jan 12, 2014)

I am at 42K B2B is gone my friend! I just love GM anymore...
[h=3]Powertrain Coverage[/h] In addition to the 3-year/36,000 mile protection, many of your powertrain components are protected even further with coverage extending to 5 years or 100,000 miles, whichever comes first.


*Transmission/Transaxle*


Transmission and transaxle coverage includes all internally lubricated parts, case, torque converter, mounts, seals and gaskets, as well as any* electrical components interna*l to the transmission/transaxle. Also covered are any actuators directly connected to the transmission (slave cylinder, etc.). Exclusions: Exclusions from the powertrain coverage include cooling lines, hoses, radiator, _*sensors, wiring, and electrical connectors*_. Also excluded are the clutch and pressure plate, as well as any Transmission Control Module and/or module programming.

So if the electrical component is internal it's covered...but and sensor, wiring, and electrical connectors and excluded? WTF?


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## ChevyGuy (Dec 13, 2014)

Looks like either wiring or bad sensor. Doesn't look like a major project to change. Just have to remove the wiring harness bracket for access. Make sure to use a new O ring.


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## Jim Frye (Mar 16, 2011)

Are wheel speed sensors involved here?


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## nuclearsteel (Jan 12, 2014)

An update!

So on the way home the CEL came on again...when I got home with a good light I saw the problem right away. The 3 wires and loom from the transmission speed sensor to the main wiring harness was mangled. All three wires and the loom were severed. 

So what was the cause you ask? Rats? Chipmunks? Hilary Clinton? Well...after removing the end of the connector, soldering in new stranded wire with heat shrink and then recovering with new loom, I had to reroute the wires into the cable tie holders...which of course I cut because I assumed (yea I know) that you could simply slide new ties thru a slot and be good to go. Then I see they are molded and I need new fancy molded zip tie wire loom holders. So I go take a bracket off that has 3 of the holders on it (2 for the cable I am working on) and 1 for a massive loom that runs to the firewall. Then I see why these ties are there...the linkage for the shifter goes right over the bracket and thus my wire and then into the tranny. I get my son to shift gears and watch the linkage move like a guillotine over the bracket and my speed sensor cable. 

I am 99% sure that something moved or caught (wire loom or more likely the tape around the wire loom) and I am running thru gears and BINGO that is what mauled my transmission speed sensor. So tomorrow I am off to the stealership to find 2 of these fancy molded wire ties. Looks like GM engineers did it again! 

If you have a car with a manual transmission you may want to check this area out! I bet if everything is perfect there will be about 1/8" clearance...best case.

If anyone is interested I can post some pictures of this half a$$ed setup.


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## nuclearsteel (Jan 12, 2014)

Here is the bracket I am talking about...anyone have an idea of what those wire tie looms are called??


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## nuclearsteel (Jan 12, 2014)

here is what I think the caused the problem...when you shift gears the whole assembly moves around the pivot. RIGHT over the wire loom for the speed sensor cable. As I mentioned above, I would bet money the loom or tape on the loom got caught when shifting.


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## nuclearsteel (Jan 12, 2014)

here is an out of focus (sorry I was pi$$ed) picture of the damage. I wire tired the line side wires out of the way...hopefully nothing shorted.


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## ChevyGuy (Dec 13, 2014)

Jim Frye said:


> Are wheel speed sensors involved here?


No.


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## ChevyGuy (Dec 13, 2014)

nuclearsteel said:


> The 3 wires and loom from the transmission speed sensor to the main wiring harness was mangled. All three wires and the loom were severed.


Well, THAT will do that ......

Good job!


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## nuclearsteel (Jan 12, 2014)

Looking for some advise! I got the wires replaced (soldered a split on each wire and heat shrinked 2x). I left a temporary hook up on top where the 3 wire feed ties in to the main harness to ensure all worked before soldering it and finishing it up. I was surprised to see that when I started the car up the Check Engine Light was still on. I unhooked the temporary hook up and check continuity to sensor. All was good. Hooked it back up and CEL is still on?

Does the CEL take so many cycles to clear? Do I have to reset it? I am typically do not like resetting CEL codes when I know what the problem was...the car resetting it tells me it is fixed. Advise?


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## ChevyGuy (Dec 13, 2014)

I'm not sure. You may need to drive it a bit for the car to figure out everything is OK again. A trip around the block should be enough for it to see that. The car may have to be in gear and rolling for the test that detects failure to run (and pass) again.


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## nuclearsteel (Jan 12, 2014)

ChevyGuy;1speedometer6 said:


> No.


So.."No" isn't completely the correct answer with respect to the wheel sensors.

The car compares the wheel speed sensors to the transmission speed sensor. 

The transmisson speed sensor seems to play a key part in the speedometer reading...but it isn't the only factor. How do I know? Because when my transmission speed sensor wiring was completely cut the.speedometer read zero when moving for a bit and the engine ran poorly...then the speedometer came back and the engine ran decent (not perfect...but like in a limp mode). 

Car had to be using the wheel sensors because that is all that was left. It certainly appeared to switch.


Also...when the speedometer was not working for about a mile, the steering was jacked! When replacing and rerouting I noticed the steering is electric...guess that explains the steer issue. When the speedometer came back the steering was much better too.

I have to say...I am disappointed of the stupid wire routing that caused the issue, but I am impressed with the redundancy and programming that made the car safe and drivable while without the transmission speed sensor.


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