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Old 05-01-2011, 10:37 AM   #1
geno607
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Default U2105 and P1780 codes

Have been battleling with these two codes all week. Have checked grounds ond connections on both ECMU and TCM, Engine cranks but doesnot fire. Plug in the scanner, get these codes, clear them, sometimes it will start, most timesw does not. Have disconnected battery over nite, still same issues, Any suggetions??

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Old 05-01-2011, 03:11 PM   #2
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Default Re: U2105 and P1780 codes

Welcome to Saturnfans!

Umm, unless you give up some more information no one here has a clue of what you're driving. I will be extremely interested if this were a locomotive gas turbine engine question; I'll be sitting in a front row seat just waiting for the brains to engage in discussion as I'll be totally fascinated with the information exchange..........................

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Old 05-04-2011, 11:01 AM   #3
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Default Re: U2105 and P1780 codes

It's a 2002 Saturn L300. I replaced the main Relay, GM of course, no aftermarket here. I read that the relay could cause this code if bad, I checked and found an after maket relay and replaced it. tested, same thing less the P1780 code.

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Old 05-04-2011, 11:54 AM   #4
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Default Re: U2105 and P1780 codes

Presuming all fuses have been checked, inside and out.......

With an L300, engine cranking but never firing up, usually means a failed crank position sensor (CPS). Next to the oil filter housing. If you have a multimeter you can disconnect it and measure across the two wires; resistance should be between 700-1200 ohms. An open reading is a failed sensor. Buy it from any auto store. If you read about dead engine starts from past threads you'll see a recurring theme about cps failures. To be sure this is an ignition related failure and not a security or fuel issue, do these checks.

Be sure during starting that the security indicator is turned off and neither flashing nor on. With the ignition turned ON, listen for the faint hum/hiss sound of the fuel pump running for 2-3 seconds then locate the fuel test valve on the fuel rail over the engine, remove the black plastic dust cap to reveal a schrader valve (resembling a tire valve), cover loosely with a rag while depressing the valve stem expecting a healthy spray of fuel. Fuel spraying means the entire fuel system is operating correctly.

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Old 05-04-2011, 04:06 PM   #5
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Default Re: U2105 and P1780 codes

And the CPS can work sometimes and sometimes not? And if bad will give me a U2105 DTC? Okay, I will try the CPS. I hope this works. At this point, the car will fire, after I switched out the relay it would not. And then it decided to work, cleared the codes and seems ok. Just very weird.

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Old 05-04-2011, 04:47 PM   #6
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Default Re: U2105 and P1780 codes

I'm not sure of what 'main relay' was replaced. Would you describe this relay and where its located? And what the actual name is used to describe it if not a main relay.

There are two failure modes occurring in cps'; intermittent and outright. Outright failure is simply characterized as the starter will turn the engine over but the engine will never fire up. Intermittent failures occurs mostly when the engine warms up to operating temperatures and then kills the engine, requiring a cool down period before allowing the engine to start/run again, only to kill the engine when warmed up. This repeats with more frustration until the cps is replaced. Heat damage.

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Old 05-05-2011, 06:44 AM   #7
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Default Re: U2105 and P1780 codes

The main relay that was replaced is under the hood in the fuse box. As of this am, car would not start right away, after a minute or so of attempts, it finally fired up, runs okay, but shifts really hard between gears. maybe need to find a priest and have an exorcism performed as I believe the car is possessed.

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Old 09-21-2012, 04:59 AM   #8
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Default Re: U2105 and P1780 codes

Resurrecting a dead thread since it bears some relevance to my life... My car has been showing a particular pattern. My car is a 2001 LW300.

The first sign of the problem is when I am unable to unlock the car with the RKE. I have to unlock it manually with the key, and the alarm doesn't go off when I start the car. Only once did I have trouble starting it when it cranked for a long time before starting, otherwise the problem doesn't affect the car's starting or running. Once it starts, the dashboard is lit up like a Christmas tree.... the Security light, the SES and Check engine lights, the ABS light. Once started, the car runs fine other than shifting hard. Sometimes the problem resolves the next time I start it, other times it takes a few starts and shutoffs before it goes away. I get the same two codes when scanned.

...
Saturns:
1993 SW2 MT 181,000 hard Boston city miles ("Rozzie")
Gone but not forgotten:
2001 LW300 ("Elle")
1999 SW2 MT
Project cars:
1966 Corvair Monza convertible
1928 Ford Model A Tudor Sedan

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Old 09-21-2012, 01:23 PM   #9
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Default Re: U2105 and P1780 codes

RKE and xmas lights are bcm related. The rest may be coincidental and related to possibly a faulty battery? If the battery is over 4yrs old, have it tested. Cheaper to replace a battery than bcm failure.

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Old 10-09-2012, 09:12 PM   #10
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Default Re: U2105 and P1780 codes

Thanks for the tip Fdryer. The reason I haven't responded is that I haven't done anything about it yet. I did have the battery tested not too long ago... What do you think about taking off the positive cable and cleaning up the leads on it?

...
Saturns:
1993 SW2 MT 181,000 hard Boston city miles ("Rozzie")
Gone but not forgotten:
2001 LW300 ("Elle")
1999 SW2 MT
Project cars:
1966 Corvair Monza convertible
1928 Ford Model A Tudor Sedan

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Old 10-10-2012, 04:57 AM   #11
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Default Re: U2105 and P1780 codes

Yes, remove and inspect both battery cables (be sure to remove battery negative 1st and put it back on last) for hidden corrosion under the heavy insulation. If you've been here long enough, you may have come across early L200's either faulty RED positive battery cables or short lengths that were either over tightened or had battery terminal failure with the side posts - once cracked, battery acid leached out and capillary action allowed acid to be drawn into the cable terminal to eat away copper wiring slowly destroying the cable connection. Reducing the gauge size from acid attack loosened the connection internally and resulted in dead battery symptoms. Some members wound up paying several hundred dollars for dealer repairs instead of attempting home inspection to remove and clean or replace battery cables and battery.

If you have to, cut away the heavy insulation covering the battery cable terminals to reveal whether or not acid damage has entered into the wires. A warm solution of baking soda and water with a tooth brush will dissolve and neutralize acid by bubbling up. Rinse with plain water. Refrain from getting this mixture into the battery vents otherwise it will neutralize battery acid and kill the battery. Clean everywhere as bubbling is a sign of acid deposits as it vents from normal engine running heat/cool cycles. If you can determine that copper was dissolved by acid, replace the battery cable. There are spray treatments for this and is basically baking soda mixed with light grease. Over tightening side terminals isn't necessary and cannot take the abuse top posts take.

If battery connections won't correct the flashing lights try pulling bcm fuses for a minute and see if this can reset the bcm.

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Old 10-11-2012, 12:03 AM   #12
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Default Re: U2105 and P1780 codes

X2 on the battery cables

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Old 10-11-2012, 03:40 AM   #13
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Default Re: U2105 and P1780 codes

Thanks Fdryer. I will try to do this sometime in the next few days and report back. It hasn't acted up in a while, but it likes to do that at the least opportune time.

...
Saturns:
1993 SW2 MT 181,000 hard Boston city miles ("Rozzie")
Gone but not forgotten:
2001 LW300 ("Elle")
1999 SW2 MT
Project cars:
1966 Corvair Monza convertible
1928 Ford Model A Tudor Sedan

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