Check engine light turn back on after repair was made

P0336 - Crankshaft Position Sensor A Circuit Range/Performance

What was the diagnosis and what was replaced? Were there any symptoms other than the Check Engine light?

This common misconception is diagnostic fault codes never say to replace a part or that one is defective. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When a part is referenced in a fault code, as in the 336, the sensor is responsible for it perhaps as much as 50 percent of the time. First we have to rule out wiring and connector terminal problems, and mechanical problems associated with that part, before we spend your money on the new sensor.

The best way to approach this is to use a scanner to view live data while the engine is running, and watch the sensor's signal while you wiggle wire harnesses and move things around to see if you can make that signal cut out.

Another cause of this code is stray signals mixing with the sensor's signal and confusing the Engine Computer. To find that, you need a scanner with "record" capabilities or one that can access the stored data in the computer. With the recording function, you erase the fault code, then go on a test-drive. When the problem occurs and the Check Engine light turns on, you press the "record" button on the scanner. Because the data passes through the scanner's memory, the recording actually begins just before you pressed the button. Later, you can play that back slowly while watching to see what changed.

Look for spark plug wires that are arcing, and look for wire harnesses that have been relocated from their original orientation. GM has also had a lot of trouble with their generators starting with the '87 model year. Due to their design, they develop a lot of voltage spikes that can damage the internal diodes and voltage regulator, and interfere with computer sensor signals. One way to identify that is to unplug the small connector on the back / side of the generator to disable it, then go on a short test-drive. Be aware the battery will be running down very quickly. With a good, fully-charged battery, limit your test-drive to ten to fifteen minutes to be safe.

These generators have had a really high failure rate. It's not uncommon to go through four to six replacements in the life of the car. The battery is the key component in damping and absorbing those harmful voltage spikes, but as they age and the lead flakes off the plates, they lose their ability to do that. Any time you need to replace the generator, always replace the battery at the same time, unless it is less than about two years old. The old battery will work fine in an '86 or older car. You probably won't identify this cause with most scanners. You need a graphing scanner that lets you watch the sensor's signal and see if other extra stray pulses appear randomly. Life gets a lot easier if you can see those stray signals, and how they're affected when you move things around that makes them worse or go away.

This is a new problem so you should start a new question. When you piggyback on this one, it was a private conversation between the two of us. As such, none of the other experts are going to see this new problem or have a chance to reply. That may not get you the help you need. Here's a link to start a new question:

https://www.2carpros.com/questions/new

You can copy and paste your post so you don't have to retype everything, but please understand you need to include a lot more information for someone to figure out if it is something they can help with, and to know where to start the diagnosis. We want to know why you replaced the battery. Was it in an attempt to solve this problem, or did the problem first occur after the battery was replaced, and if so, right away, or hours, days, or weeks later?

Why did you replace the starter? If you think the generator is okay, tell us what tests you did or any observations that led to that so we feel comfortable assuming the same thing.

Be real specific with the symptoms and anything related that led up to this problem. All I have to go on is the two parts, but no symptoms. I'd have to guess the starter isn't cranking the engine, but do you have dash lights, radio, dome lights, etc? If everything is dead, as might be with a bad battery, you can't expect the starter to work when nothing else does. There's thousands of parts in the electrical system. Any one of them can cause similar problems, so just because you replaced two of those parts, you can't expect that to solve a problem unless some diagnostic tests led you there.

Now that I shared all that wondrous information, I'm going to start with assuming everything is dead. You'll need a voltmeter to make some basic tests around the battery, then we'll know where to go next. If you don't have one already, Harbor Freight Tools has a perfectly fine meter for less than ten dollars. You can find them at Walmart, any hardware store, and any auto parts store too, although you'll pay a lot more at auto parts stores. You can go here:

https://www.2carpros.com/articles/how-to-use-a-voltmeter

to see how to use the meter, but this article shows using an "auto-ranging" meter. Most inexpensive meters don't have that feature. I can help you set up and use a regular meter if necessary. We would normally start by measuring the battery's voltage. If you connect the meter's leads backward, that won't hurt it. You'll just get a minus sign in front of the numbers. A good, fully-charged battery will read close to 12.6 volts. If you find it's around 12.2 volts, it's good but fully discharged. When you find it around 11 volts or less, it has a shorted cell and the battery must be replaced.

There's more places to take readings, but until I'm sure of the exact symptoms, one thing that is real common on all car brands is a loose connection at the under-hood fuse box. If you look at the cable connected to the battery's positive post, there's one really fat one going down to the starter. Follow the other, smaller wire to that fuse box. That is the connection that often works loose. On most car models everything will be dead, but there are a few models that have some dash lights that still work. Another common observation is the dome lights, dash lights, and everything else appear to work okay until the ignition switch is turned to "crank", then everything goes dead. Typically people report the lights will work again after letting the car sit for an hour or more. That's another way that bad connection at the fuse box shows up.

If that doesn't help, consider posting the new question so everyone can read it. If you do solve the problem, please be sure to post a follow-up reply with the solution and how you figured it out. That tells us it has been handled, and it helps others who are researching a similar problem.