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Random/multiple cylinder misfire, injector circuit malfunction in cylinder three and system voltage low

Tiny
MIKEYWARD865
  • MEMBER
  • 2005 JEEP LIBERTY
  • 4.0L
  • V6
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
I was driving down the highway and the hose from my overflow tank came lose and threw coolant all over the passenger side of my motor. I fixed the hose and refilled my coolant. When I started it back up it was misfiring bad and would not stay running when I would put it in drive and try to take off. I bought a code scan tool and scanned my car and it throws 3 codes consistently over and over.

1) P0203: Circuit malfunction cylinder number three.
2) P0300: Random/multiple cylinder misfire detected.
3) P0562: System voltage low.

What do these codes thrown together mean is wrong with my vehicle?
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Saturday, November 2nd, 2019 AT 9:30 PM

16 Replies

Tiny
MIKEYWARD865
  • MEMBER
  • 16 POSTS
It is actually a 2007 not a 2005 with a 3.7l engine. It has thrown 5 codes total p0203, p0300, p0562, p0731 and p0736.
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Sunday, November 3rd, 2019 AT 1:41 PM
Tiny
MASTERWRENCH
  • MECHANIC
  • 258 POSTS
Based on that list of codes, it would appear there is an issue with injector #3 or the wiring for it. It's more than likely the cause of the other codes. The low voltage code may have set when coolant got on the serpentine belt which could have caused it to slip, preventing the alternator from charging properly. I would start by removing the injector #3 connector and checking for coolant contamination. Injector #3 will be the middle cylinder on the driver side.
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Sunday, November 3rd, 2019 AT 5:46 PM
Tiny
MIKEYWARD865
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How can I tell if the injector has gone bad?
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Monday, November 4th, 2019 AT 8:51 AM
Tiny
MASTERWRENCH
  • MECHANIC
  • 258 POSTS
The best way to test an injector is by measuring its resistance. Attached is a chart from the service information indicating what the resistance value should be at varying temperatures. You should be looking at a value somewhere around 12 ohms.

Take a look at the article below for a more detailed procedure for how to test a fuel injector.

https://www.2carpros.com/articles/how-to-test-a-fuel-injector
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Monday, November 4th, 2019 AT 10:18 AM
Tiny
MIKEYWARD865
  • MEMBER
  • 16 POSTS
Okay, I took off all the connectors to the fuel injectors and cleaned them out. Now the only codes it is reading is p0300 multiple misfire and p0562 low voltage.
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Monday, November 4th, 2019 AT 3:00 PM
Tiny
MIKEYWARD865
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  • 16 POSTS
I had a friend of mine say it could possibly be a bad alternator. Do you think that could be possible?
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Monday, November 4th, 2019 AT 3:01 PM
Tiny
MASTERWRENCH
  • MECHANIC
  • 258 POSTS
A failed alternator could certainly cause the system voltage to be low, but I wouldn't expect that to cause an issue with a single fuel injector. If you want to verify whether your alternator is charging properly, take a look at the test procedure in the link below.

https://www.2carpros.com/articles/how-to-check-a-car-alternator
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Monday, November 4th, 2019 AT 5:45 PM
Tiny
MIKEYWARD865
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It is no longer throwing a single misfire code only the multiple random misfire code.
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Monday, November 4th, 2019 AT 6:57 PM
Tiny
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So at this point, P0300 is the only code set? Nothing else? Does the engine appear to be running rough at the moment?
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Monday, November 4th, 2019 AT 8:26 PM
Tiny
MIKEYWARD865
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Yes, it still runs very rough and it is throwing the low voltage code with the p0300 and p0562. I reset and re-scanned multiple times to be sure.
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Monday, November 4th, 2019 AT 8:32 PM
Tiny
MASTERWRENCH
  • MECHANIC
  • 258 POSTS
At this point, I would focus on the low voltage code as it's continuing to reset. If the system voltage is too low, there may not be enough current to properly fire the coils and/or injectors. This makes more sense at this point vs. The single cylinder injector code. Let's perform the alternator test as discussed earlier and see what the results are.
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Monday, November 4th, 2019 AT 8:41 PM
Tiny
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Can a loose serpentine belt cause both misfire codes and fuel injector codes?
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Sunday, November 24th, 2019 AT 2:10 PM
Tiny
MIKEYWARD865
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Also could it being out of time cause misfire codes and fuel injector codes? I took my alternator and had it tested and it's good. I also took all my spark plugs out checked the gap and cleaned them with a wire brush.
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Sunday, November 24th, 2019 AT 5:17 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,014 POSTS
The loose belt could cause the low voltage code but it won't set the injector or misfire codes directly. The low voltage however could cause those because the PCM expects to have a set voltage to work with and anything that disturbs that can cause problems. Low voltage on that vehicle can be caused by multiple things with the alternator being one of the lower reasons. That is because the alternator charging isn't controlled in the alternator but inside the PCM. The only way to tell if there is a charging issue would be to test the entire system, not just the alternator. If you have a voltmeter you could check at least that voltage and get an idea of the issue. With it you should have about 12.6 volts with a fully charged battery. Then start the engine, while it is cranking the voltage shouldn't drop much below 10 volts and once it starts running the voltage should jump up to 13.6 - 14.7 as the battery charges. If the light is still on with those voltages then it may be an internal PCM error.
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Wednesday, November 27th, 2019 AT 10:03 PM
Tiny
MIKEYWARD865
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Okay, how much would it cost to get the system checked somewhere? I don't care to try and do it myself but I want to make sure it's done right. And nothing gets missed.
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Friday, November 29th, 2019 AT 6:27 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,014 POSTS
Well the chain stores claim they will test the charging system for free. Might give that a shot first, the newer digital testing machines do a pretty good job. The operator sets the battery type and rated amps and connects it up. Then it's just follow the instructions as it tests. Hard to mess them up. But to test if it's actually low voltage even a cheap multi-meter would do that.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

https://www.2carpros.com/articles/car-battery-load-test

It could be something simple like a bad connection or bad ground throwing the entire system off.
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Friday, November 29th, 2019 AT 7:34 PM

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