LS2 2000 bad battery no start
 

2000 saturn LS2 sedan V6 Had bad battery had to jump start the car. Car started but service light came on. car would turn over but not fire. Read could reset comp by disconnecting the + and - cables from battery and touch them for 2 min. After that car started immediately and runs fine. Prior to new battery my innova 3100 scanner and mechanics scanner would not connect. Still would not connect after new battery. After running drive cycle and resetting service engine light by disconnecting the fuzes to ecm and ign and putting them back car ran for three days just fine. Auto zone connected ran three codes.P1780,P0601and U2105. Again after three days car would turn over but not fire.Disconnect =and - cables to battery and touch together for 2 min , car started just fine but service engine back on. ran codes at autozone same three error codes.
any ideas.
casey9941

related to no start after bad battery
 

Found out that if you remove 10 A BCM/ECM/Cruise/ABS fuze(under hood panel) you must disconnect battery cables and touch = to - for 2 min to get vehicle to start. Or wait until after drive cycle,3 days and car will turn over no fire. Touch cables starts rifgt away???? casey

Likely a communications issue between ECM and other modules, including the BCM.

Something is flaking out when trying to communicate. Pulling the BCM fuse will allow the BCM to " completely reinitialize" itself at next key ON. Totally disconnecting battery cables and touching them brings everything to ground potential. This clears out all volatile memory in the ECM. At next key On, Everything communicates properly and the car starts and runs.

Your diag port included.

Eventually, some communication becomes corrupted and the modules no longer can communicate. ECM and BCM must communicate for car to start and initially run.

P1780 is for the Park/Neutral Position [PNP] Switch Circuit which may mean the sensor in theory. It can also set if the TCM requests a torque reduction and the ECM fails to comply. The most likely reason for failure to comply? Garbled communication between the modules (TCM and ECM or ECM and BCM).

P0601 is defined as a Internal Control Module Memory Check Sum Error

The PCM or Power Train Control Module performs many vital functions in a modern vehicle, such as management of the Fuel System, Ignition System, Transmission, Anti-Lock Brake and Traction Control systems. The PCM regularly runs a self-diagnosis function where it performs normal mathematical calculations, and if the results of these calculations are not as expected, a code such as P0601 code will be set.

This does NOT necessarily mean your ECM is toast.

Common Problems That Trigger the P0601 Code

• Lack of proper voltage to the PCM
• Defective PCM memory module
• Defective PCM ground circuit(s)
• Defective PCM controlled output devices

Common Misdiagnoses

• PCM is replaced when the root cause is improper voltage to the PCM
• PCM is replaced when the root cause is defective PCM ground circuits.

If the ECM is not receiving sufficient current at the right voltage, it will likely malfunction so a P0601 is not a surprise. Nor is it a surprise if ECM grounding issues exist. Other devices controlled by the ECM can malfunction and drag down the voltage to unacceptable levels which lead to malfunctions. ECM communication malfunctions are not out of the question.

DTC U2105 sets when a specific controller has lost communications with the ECM.

Common theme, no?

See https://www.justanswer.com/saturn/2xoml-need-know-wut-code-means-sae-u2105-car-will-not-start-ran.html for a beautiful description of the communication set up and troubleshooting flow diagram.

Please keep us informed.

Checked all the grounds I could find, no improvement. Too to chevy dealer and had it diagnosed. Bad ECM. Fladship one on internet had part # 9153242 for $150 lifetime guarentee preprogrmmed.( you will need to program your Key)
Awaiting part will let you know
casey9941