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I tried to start my c7 this morning and it would turn over but not start. I got the reduced engine power light. I checked the codes and got about 6. I jumped the car to get it started and now the only codes it shows are P0192, P0641 and no DTC reference. Could a bad battery cause this? I multi metered the battery and it was 12V but I did have a charger on it for awhile before that. Some of the codes when it wouldn't start were the ones mentioned and then one about camshaft position. and atmospheric pressure and fuel rail pressure but those are gone now. I do have a supercharger on and had the tune tweeked about 2 weeks ago for living in a new elevation. But I drove the car almost everyday after that retune and all seemed good till now. So wondering if its the tune or the battery or a mechanical issue. Any ideas? Thanks.
I know the battery can and will cause all kind of fault codes if it is weak. Many members tested their batteries and all seemed good. Changed the battery and all things became good.
P0641 is a DTC that indicates the ECM has detected a short to ground or voltage on the 5V Reference 1 Circuit for greater than 0.5 seconds. The 5V Reference 1 Circuit feeds the following sensors: AC Refrigerant Pressure, Camshaft position sensor, Fuel pressure sensor, Fuel rail pressure sensor, Fuel tank pressure sensor and the Multifunction intake air sensor.
P0192 is a DTC that indicates the ECM detects the fuel rail pressure sensor 1 signal is less than 0.25 V for greater than 2. 5 seconds.
With the P0641 code it is easy to see why the engine cranked (turned over) but didn't fire since the key sensors needed for it to fire weren't getting the proper voltage.
The battery or battery connections may have had something to do with these two codes showing up. P0192 probably shows up because a short to ground (or low voltage, a short can be interpreted as 0 volts) occurred on the 5V Reference 1 Circuit. Overall, most battery issues are caused by battery connection issues and circuit ground connections. When you jumped the battery you bypassed any connection issues on the battery posts by directly connecting to the cables.
Inspect the battery connections to see if they are loose or for corrosion around the battery terminals before replacing the battery. Sometimes all you have to do is clean and tighten connections properly Vs replace the battery which ends up doing the same thing at a much higher price. If you have a circuit ground connection issue a new battery won't resolve the issue since replacing the battery doesn't resolve the ground issue. If you have good connections and still have starting trouble then it is time for a new battery. Poor connections add resistance to current flow and increase voltage drop in the circuit and as the battery ages it will decrease its output voltage to some degree. In a circuit without the added resistance the slightly lower battery output will let a battery keep powering the car for months to years longer than a lot of people think they can. I for one would take the car out for a 30 to 40 mile highway drive to see if the battery charges properly and to see if it holds the charge over night before replacing the battery.
You find things like this out when you drive your car to work on a cold winter morning and it won't start after sitting outside in the cold all day. Then you are left using the security shack's car starter and tools to clean battery terminals and jump start the car in the dark while being dressed in your suit and maybe with a topcoat and hopefully some gloves. Freeze your butt off like that one or two times and you make sure the battery terminals are clean.
Bill, all connections to the battery were clean but cleaned again and tightened down. I multi metered not only the posts but also the cables going out and all good. Is there a place in the engine I can put the multi meter to and see that its getting full voltage up? And is there a fuse related to the areas you mentioned? Thanks.
And Im assuming that if I can jump the car then as you say I am bypassing some areas and with the battery holding its charge then its probably in the engine bay?
OK so another update. I jump started the car and it was in reduced power mode but everything sounded good and it drove fine up to 25 mph. Drove around for about 10 mins came back home and stopped the car. Waited about 10 secs and started the car again and it started but again in reduced power mode. Im sure in the morning it wont start again but will see. So if I can start it after being jumped does that mean its the battery even though the battery read 11.94 with the car off and 14v with the car on? Or can circuit A still have an issue?
Pretty sure the battery should read in excess of 12V when the car is off..
Given the connections are clean and tight I agree that if the battery is less than 12V then the 5V references the ECM establishes for the engine sensors can be wrong and you get the reduced power or no start condition. However, using voltage to determine the battery's state of charge can be erroneous if you don't wait a minimum of 12 hours after the battery has been used or charged. That also means that all parasitic loads must be shut down before the battery state can be checked. The FSM provides the following procedure for determining State of Charge:
Based on your 11.94 V measurement it surely seems like your battery needs to be replaced. However, there is one other thing to consider before replacing the battery. Was your 10 minute drive long enough at a high enough rpm to recharge a severely discharged battery? On a charger sitting in the garage it might take 24 or more hours to recharge the battery depending on the capacity of the charger. A severely discharged battery can take more than twice as long to recharge than a battery that isn't severely discharged.
Bill
Last edited by Bill Dearborn; 12-10-2018 at 11:41 AM.
Given the connections are clean and tight I agree that if the battery is less than 12V then the 5V references the ECM establishes for the engine sensors can be wrong and you get the reduced power or no start condition. However, using voltage to determine the battery's state of charge can be erroneous if you don't wait a minimum of 12 hours after the battery has been used or charged. That also means that all parasitic loads must be shut down before the battery state can be checked. The FSM provides the following procedure for determining State of Charge:
Based on your 11.94 V measurement it surely seems like your battery needs to be replaced. However, there is one other thing to consider before replacing the battery. Was your 10 minute drive long enough at a high enough rpm to recharge a severely discharged battery? On a charger sitting in the garage it might take 24 or more hours to recharge the battery depending on the capacity of the charger. A severely discharged battery can take more than twice as long to recharge than a battery that isn't severely discharged.
Bill
I agree, and good point about the short trip. Maybe he could borrow a friends trickle charger and leave it on there over a few days and see how it does..
I did have the battery on a battery charger over night at one point and it still would not start so its looking like a bad battery. Just need some time away from work to get it replaced. Will post results when I get it replaced. Im in Hawaii now so Im sure the battery is just as expensive as everything else here. lol.
12-07-2018, 11:37 PM
Engine code p0192, p0641
