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Buzzing along happily at Charlotte Motor Speedway, screaming down the front straight - got the reduced power console message, engine died entirely.
Thankfully I was near a turn into the paddock area.
Two of the SCCA track workers pushed me off, did not even need a tow!
Would not start, turned over and snorted/coughed, but, that was it.
P0651 5-Volt Reference 2 Circuit ECM
I don’t see where this code has happened much in the forum.
Not seeing anything in the factory manual for P0651.
I got the P0651 code from my OBD reader, not the Tech 2.
My OBD reader description is “Sensor reference voltage B circuit/open”
Got the “5-Volt Reference 2 Circuit ECM” code description from a post by @Dano523
I’ll put the Tech 2 on it this morning and let you know what I find out.
hope everyone has a great day!
Thank you for taking a peek at this post.
Greg
Probably one of the sensors on that “circuit 2” pulling down the 5 volt reference to ground…can’t remember off the top of my head which sensors they are…sometimes looking at scan data for those sensors may help !!…look for a voltage parameter that looks abnormal on circuit 2 or start disconnecting sensors or looking for a short to ground on that sensors wiring…the 5 volt ref can be compared to your heartbeat…that goes down and you go down !!
Put the tech 2 on it - it also had a P0335 for the Crankshaft Position Sensor Circuit - reference 1 was 5V, reference 2 was .6V
I'm going to get the car off the trailer and onto the lift to run thru the troubleshooting procedure for the CKP sensor from the service manual and see where that leads.
Thanks for the help @C5 Diag !
Great !!…had to edit this post…the CKP sensor is a 3 wire Hall Effect sensor…12 volt power, a signal (the 12 volt signal gets pulled to ground by the crank reluctor), and a ground !!…I’m pretty sure your model year does not have a 5 volt ref on the crank sensor !!..will have to see what other sensors on circuit 2 with a 5 volt ref.
Finally was able to drop the starter and get to the connector.I’ve got a picture of the connector in the car, there are two connector representations for the CKP in the factory service manual.The measured voltages L-R: 5V, .03V, .78V
So I’m confused now.
The first wire looks to me to be a black with a yellow stripe.
I did get the replacement OEM part from the dealership off a VIN look up. But the part number on the sensor I removed (12585546) is different than the new sensor p/n (12703627), however, they do appear to be the same on rockauto site - they’re listed together on the replacement parts.
The 12585546 part number does not come up on a search at parts.chevrolet.com
The Chevy parts site lists 12703627 - hunting around quite a bit, it appears that this is a replacement/supersede P/N
My gut is telling me that my wiring is fine. And that pin A is the 5 V reference.
Photo diagram is looking at the end of the connector, wires away from you, and connector clip upwards. So above does match what you have on hand.
So C pin should be 5 volts into the sensor with ECM energized. If no power, then start checking its wire from pin end to pin end to see if it's cracked somewhere or at the pin connectors.
B is the low reference that the sensor sends back to the ECM to show that its there when the system is energized.
A is the sensor signal off the 5volts back that ecm when it picks up the notch each time.
So if you have 5 Volts on the C pin, and the ECM is telling you that the sensor is bad, then its the B wire that you want to check end to end, to make sure it not cracked.
If not cracked, then bad sensor.
I just realized that part of my confusion was I had the camshaft connector diagram and the crankshaft diagram.
I will go back and check it again, but I was measuring L-R, A-C: 5V, .03V, .78V
which seems reversed from what I should be measuring,…
I’ll check them again!
thank you!
Greg
I’m assuming you have a scan tool so unless it’s a cheap code reader you should have a data PID for both 5 volts circuits and you should be able to see what your ECM is seeing as far as your circuit 1 voltage…I really wouldn’t worry about the low ref (ground) or the sensor signal wire when the sensor is unplugged…I’m out of town so I don’t have access to check the other sensors that are on circuit 1…you will need to know this in able to diagnose this !!
Rechecked the Voltages at the connector, all good - I wasn’t making good connections with the probes.
Replaced the crankshaft position sensor.
Ran the Tech2 checked reference voltages and the 3 sensors on the 2nd ref circuit.
all came back 5V
Cleared all the codes
bolted it all back up and it started. Yeah!
On the 2nd start I’ve got a P0030, heater circuit bank 1 sensor 1, again, ugh!
I’ll take it for a drive to see what else pops up.
I was working on a multitude codes from the front O2 sensors, C6 Z06 track car. The headers were one of the worst fitment I've seen, heat in that area of wiring between firewall & starter is brutal.
I've melted wring back their on the dyno not paying attention. I'm wondering if your issue may be heat related & in the early stages. I did read you do not believe it is a wiring issue.
I was working on a multitude codes from the front O2 sensors, C6 Z06 track car. The headers were one of the worst fitment I've seen, heat in that area of wiring between firewall & starter is brutal.
I've melted wring back their on the dyno not paying attention. I'm wondering if your issue may be heat related & in the early stages. I did read you do not believe it is a wiring issue.
I had a short on the extension where the shop had wire tied it up really tight, split one of the wires and it was arcing to the tunnel shielding. That was a bear to find.
I've been progressively getting better about recognizing wires getting a bit too tan
So, point very well taken. I need to protect those wires, so, I'll check it out.
This time the heater is what's dead in the O2 sensor - pulling 0A off the Tech2 reading. All other checks came back fine.
I'll replace the sensor here in a bit and check all the wiring and shield it better.
Thanks for the comments!
I replaced the O2 sensor and checked the heater circuit on the sensor, it was an open circuit.
No 02 sensor errors when I started it up and idled it for several minutes.
However,.....
The saga continues -
I pulled out to fill it up with gas and didn't get into 2nd gear before it went into reduced power mode and the engine died.
Fortunately, it did restart after turning it off for a minute, I was able to drive it back to my garage.
Pulled the codes:
P0651 and P2135 (TP voltage correlation).
Something I haven't mentioned, I also have a P2068, fuel level sensor B circuit high.
It somewhat randomly fires when I get below 3/4 full, if I'm on track sloshing the gas around it never fires.
I don't know if that's relevant or not,...
It started w/o an issue several times in my garage
I put the Tech2 on it and and the 5V ref voltages are both @ 5 or 5.1V
The manual says when the throttle plate is in the closed position, the TP sensor 2 voltage should be near the 5V reference and the TP sensor 1 voltage should be near low reference.
The voltages are not making sense to me with my foot off the acc and then pressed to the floor.
The two sensors in the TB and APP (pedal position) are apposing each other for the back up cross check, so one starts high and will go lower the vain opens up, while the other starts low, and will go high for the vain postion. Same for the pedal poition as well.
As for foot to the floor, indicated potions between the two should be the same percentage wise, so would dare to guess that one of the stat pads in the TB is dirty, and it may need to be pulled apart (B motor housing) to clean it and its swiper (if you do have the skill), or may have to replace the TB isntead. GM did not use a parts replaceable position sensor in either the Pedal assembly, nor the TB, and just expect that these two assemblies would be replaceable assemblies as the sensors did start to age/get dirty and have problems.
One sensor for the TB (swiper and T stat plate) is under the gold cover plate, while the other sensor is on the bottom/inner side as yo dig deeper in removal of parts instead.
I forgot to include a small detail, I’m running a Nick Williams 103 throttle body.
I’m having a hard time trying to find the Nick Williams website, support, or any sort of service documentation on the throttle body.
Well I met Nick Williams today. His shop is a little under one hour from my home.Could not meet a nicer guy, has one amazing machine shop.I went to the front desk and asked for Nick and they looked at me like I had three heads!He came and grabbed me took me back to his workbench put it on a scanner looked at me and said everything‘s registering fine, did one more cycle on it and it did it. Voltages dropped down to nearly 0. He said that’s your problem. He replaced the electronics on the spot for me and sent me on my way.
Ominous P0651, Reduced Engine Power
