Preface: Seeing as we're getting a lot of threads in here about common issues that have simple fixes, this thread will be linked in the Table of Contents and divided into Maintenance and Aftermarket issues. If you have something to add, email me.

The FSM has in-depth instructions (with pictures) for most of these procedures and more. Get it here.

Remember to check and make sure you've accounted for all of the issues posted in Trouble Areas threads:B15B16Older Models (SR20 only)

More advanced issues may be addressed by the giant FAQ in the Nissan Online Mechanic section.

Maintenance:

Reading SES Codes Without OBDII Reader- Turn the ignition key to the ON position and wait three seconds. (Do not start the car.)- Fully depress and release the accelerator pedal five times in less than five seconds.- Wait exactly seven seconds. Fully depress the accelerator pedal for ten seconds until the MIL light flashes.- Release the accelerator pedal and start counting flashes to obtain the four-digit trouble code.

Long flashes (0.6 seconds) indicate the first digit of the code; count the blinks one through nine and write down the first digit. (Ten blinks indicates a zero.) The next three digits follow in turn in the same fashion except with faster blinks (0.3 second) and a 1.0-second pause between digits.

The ECM code repeats itself until you turn the ignition key to the OFF position, at which point the ECM resets itself to standard get-in-and-drive-the-car mode. You can look up the trouble codes in the ESM/FSM; there's a bunch of them. In the ESM, refer to page EC-639. RED_DET has posted them in this thread as well. Additionally, if you get four blinks of ten (0000), the ECM is indicating no malfunction.

Clearing SES/CEL Codes (without an OBDII reader)- Unhook one of the battery cables from the terminal- Let car sit for a few hours, or, to be sure, overnightOR- Hold down the accelerator pedal for more than 10 seconds while in Diagnostic Test Mode II. When you release the pedal, the ECM erases the trouble code(s).OR- "Natural" method - drive ~50miles with the issue fixed. Note that some codes are permanent until manually cleared one of the other ways.

Idle Relearn (do this if your idle is high and/or you get a high rpm code or any code pertaining to the TPS or idle)

- Turn ignition switch OFF and wait at least 10 seconds.- Confirm that accelerator pedal is fully released, turn ignition switch ON and wait 3 seconds.- Repeat the following procedure quickly five times within 5 seconds.a. Fully depress the accelerator pedal.b. Fully release the accelerator pedal.- Wait 7 seconds, fully depress the accelerator pedal and keep it for approx. 20 seconds until the MIL stopsblinking and turned ON.- Fully release the accelerator pedal within 3 seconds after the MIL goes off.- Start engine and let it idle.- Wait 20 seconds.- Rev up the engine two or three times and make sure that idle speed and ignition timing are within thespecifications.

Cleaning the MAF (do this if you get a MAF code or the car stalls randomly)- Grab a bottle of Windex or, better yet, MAF cleaner.- Mist over the MAF such that gravity causes the mist to fall onto the sensor - too much cleaner can damage the sensor.- Grab a Shopvac or some other blowing device and run air through the MAF chamber to dry the sensor

Car Won't Start/Electrical Is Iffy (lights dim, etc)- Use a wire brush or sandpaper on the battery terminals. All B and P chassis vehicles, especially later ones, are notorious for poor grounding and corrosion.

Brake Light On- Make sure your E-brake is completely released- Check fluid level, if it's even a smidgen low it can cause the light to stay on

QR25DE Butterfly Screws- Refer to the FSM to find out how to get to the screws, the procedure is very difficult to explain without pictures or the diagrams shown in the FSM.- Apply GREEN Loctite as explained by the instructions on the Loctite container.

Aftermarket:

SES Light Due To Header1. Move the Second O2 sensor behind the cat.- Install your header and midpipe- Plug first O2 sensor into the appropriate bung on the header- Use a bung plug to fill any other holes (except EGR where applicable)- Lengthen the wires on the second O2 sensor so it can go behind the main cat- Weld a bung into the catback where you're going to put the sensor- Plug in the sensor- Clear any existing codes or wait til they turn off naturallyOR2. Spark Plug Defouler Trick- Buy a spark plug defouler from Autozone or the like- Drill out the top end to a size that fits your sensor- Put the sensor in the defouler- Put defouler in the O2 bung*This effectively acts as a spacer between the exhaust stream and the sensor, causing it to read less of the exhaust air.*OR3. Electronic Sim- Check Ebay, install as explained. A lot of these are poorly designed, so realize that you get what you pay for. This is basically a resistor placed in the wiring that is equal to the resistance of the sensor when it is reading clean.

NOTE - Some engines (00-02 QG18DE for instance) have 4 O2 sensors, two before the precat and two afterward. Simply do one of these tricks to BOTH of the second pair of sensors, putting the two that were in the stock exhaust manifold into the aftermarket header. Also be absolutely sure not to cross the plugs on the front two sensors from how they were stock. Otherwise you will throw a circuit malfunction code, or, worse, multiple circuit malfunction codes.