P0420 code and engine is not starting.

ANSWER : Hello. Thank you for writing in. There are several reasons your vehicle may only start when jump starting. The first and most common is a build up of resistance that is causing you to need a boost of voltage to get the engine started. This may be due to poor battery cables, a bad ground connection, a poor starter solenoid, and a couple of other issues. The first thing you want to do is perform a visual inspection of the starting system. Make sure there is no corrosion build up in the battery cables. You can also check the resistance across these wires and make sure you have a solid connection between components. You then want to make sure the starter solenoid is doing its job. It is responsible for taking the small amount of electricity sent by the ignition and turning it into a huge electrical charge that is strong enough to push over the engine with the help of some gear ratios in its favor. Do some more testing, and stick to the basics before assuming its something seriously complicated.

ANSWER : Hello there, thanks for writing in. You may have a few different things going on with your 1990 Pontiac Grand LeMans. These codes are most likely all related and have a few common causes. The most likely causes for this would be a stuck, open, or faulty thermostat, coolant temperature sensor, vacuum leak, spark plugs, exhaust leak, or an oxygen sensor. A certified automotive technician such as one from YourMechanic will perform a check engine light is on inspection and diagnose the fault performing any repairs required.

ANSWER : If the mechanic tested the output (functioning) of the oxygen sensor, especially according to the protocol at this link and found that the sensor was non functioning at that time, what you might be experiencing is a "failing" oxygen sensor and so the latest instance of Code P2196 might be explained by that. A complexity though is Code P2196 has many causes other than a failing oxygen sensor including: a faulty fuel pressure regulator; MAF (Mass Air Flow) sensor; ECT(Engine Coolant Temperature) sensor or damaged ECT wiring; leaking or stuck open fuel injector or injectors; and spark plugs and/or coil pack. Basically, if the Code (P2196) recurs, the oxygen sensor output can be re-tested but the mechanic will hopefully be aware of all these other possible causes of that Code setting. If the Code recurs, you can request a check engine light diagnostic and a certified Mechanic, dispatched by YourMechanic right to your location, will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

ANSWER : Hi there. There could be two problems here. It is possible that your battery is bad and will not take a charge from your alternator while driving. In that case every time you shut your car off you will not have enough juice to start it again. Inspect your battery – it should have at least 12.5 to 13 volts to start your car, if it doesn’t you will need to replace the battery. The second problem could be that your alternator is bad and not charging your battery, in this case you will need to replace your alternator. Both the battery and the alternator can be tested in your car. If you would like to have the car checked for you, a certified professional from YourMechanic can come to your car’s location to diagnose the starting problem and proceed with repairs.

ANSWER : The code P0685 indicates a problem with Engine Control Ignition Relay Control Circuit. This may have a poor connection or need to be replaced. I would recommend having an expert from YourMechanic come to your home to diagnose and repair.

ANSWER : This may be an issue related to what is called an idle air control module. This is a module that regulates the amount of air that is allowed into the intake system as it is mixed with the fuel before being injected into the motor. When this is not working properly, this will cause the car to stall as you describe. I would suggest having an expert from YourMechanic come to your home to definitively diagnose the stalling issue and make necessary repairs.

ANSWER : Has a mechanic’s stethoscope been used to track down the specific location of the noise? There are several solenoid valves in the engine bay that do not run all the time and may be pretty loud once they start, such as an evaporative emissions purge valve and the like. The high fuel trims on one bank sound like you may have a problem on one side with a vacuum leak. A positive trim means air is being added and the computer is trying to add fuel to compensate.

I recommend having an experienced technician, such as one from YourMechanic, come to your location to determine why the engine is making a noise and suggest the proper repair.

ANSWER : It’s curious that you don’t seem to have a code in the ECM. Usually if you have a malfunction that prevents the car from starting, there will be a code resulting. That being said, it sounds like you may have an issue with a crank position sensor or an ignition control module. Both of these have a history of failing when they are hot and coming back to life again when they are cold. A bad crank sensor will almost certainly result in a code, but an ignition module might not. It’s hard to say what the issue is about the door lock, but it is probably not related.

Both of those pieces are pretty expensive, so I don’t recommend just replacing them to see if it works. Your best course of action would be to have a mechanic check it out so you don’t replace anything you don’t need. YourMechanic can send a technician to your home to diagnose the starting problem firsthand and recommend an accurate fix.