Tuesday, April 2, 2013

Why Check Engine Light Comes ON?

Check Engine Light Comes On


2001 Jeep Cherokee Check Engine Light



There are dozens of things that can turn the engine light on but if you have the Jeep near I can tell you how to read the fault codes yourself.
If we can find out what codes are stored then I can give you a much more precise idea of what is going on. There is an easy built in code read feature we can use if you're able to get to the Jeep.


HOW TO RETRIEVE THE CODES MANUALLY WITHOUT A SCAN TOOL

The Procedure Is As Follows:
Cycle the key from off to on three times ending with it on and watch the digital odometer display. Don't crank the starter, just off to on. After the last time you turn the key on the fault codes will show up in the odometer display. The codes start with a P and have four numbers, there may be more than one stored.

Get in and close the doors, put the key in and turn it one click forward. This is the off position. One click forward of that is on. Start with it off and go on, off, on, off, on within about five seconds and the odometer will change and show codes. Remember to not crank the starter, just off to on.


REASONS FOR CHECK ENGINE LIGHT ON DASHBOARD:

Issue With Computer Module


  • There are dozens of things that can cause the check engine light to come on. The light comes on because the powertrain control module (PCM) sees a problem in a monitored system or component and sets a fault code. Any sensor on the engine, transmission issues, evaporation emissions, etc will all turn the light on.


You can check the air filter if you're questioning it, but the filter won't turn the light on.

Issue With Spark Plugs

  • The spark plugs were due for replacement at 30,000 miles so if they haven't been done then a tune up is in order. That may or may not be the reason the engine light is on though. 



Transmission Gear Shift Or Solenoid Issues


  • If you aren't noticing any symptoms the you can likely rule out anything transmission related. Most problems with the trans that would cause the light to come on would also cause shift problems.


Loose Gas Cap Or Emission Issues

  • Check your gas cap to make sure it's tight. The evaporative emissions system is checked for leaks, if your cap is loose or isn't sealing correctly it will turn the light on.


Evap Leak issues

  • It could also be a leak somewhere in the system. There are vapor lines from the engine back to the fuel tank, there could be a leak in a line, the canister, or there could be a problem with the leak detection pump or purge solenoid. Evap leaks are a very common reason for the engine light to be on with no symptoms.

Faulty Or Loose Or May Be Dirty Sensors

  • Any of the sensors on the engine could turn the light on. The up or downstream oxygen sensors, throttle position sensor, MAP sensor, coolant sensor, and intake air temperature sensor could all set a code either from a failed sensor or wiring issue. Sometimes you will have symptoms and sometimes not.

Cats Converter Issue

  • Catalytic converter efficiency is monitored, if one of them wasn't passing the monitor then it would turn the light on with no symptoms.


Issue With Oxygen (O2) Sensor

  • A failed oxygen sensor will often turn the light on with no symptoms also.



Faulty Ignition Coil Issue

  • The ignition coil can cause the light to come on as well as spark plugs or fuel injectors, but these will usually cause some rough running.


Crankshaft Or Camshaft Sensor Issue

  • The camshaft or crankshaft position sensor can cause the light, but usually these would also cause some driveability problems.


Faulty Thermostat issue

  • Once in a while thermostats on the 4.0 will fail and cause excessive warm up times and this will also set a code but you wouldn't notice anything except for it taking a while longer to warm up from a cold start, or the temperature gauge not getting into the normal range.

This are the most common possibilities,that can cause check engine light to come up on dashboard.

This will help.
Thanks.


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