Check Engine Light (Malfunction Indicator Lamp) On

Engine Related Issues

By Rodney (Mechanics)

The Check Engine Light (that’s the MIL or Malfunction Indicator Lamp) notifies you if an emissions-related issue happens with the emission controls or engine control system on your vehicle. Depending on existing issue, the Check Engine Light will remain on repeatedly or flash and may appear on. Several intermittent problems could make the Check Engine Light on only when the problem is happening (for example engine misfire). The Check Engine light commonly stays on when a fault has been detected and may stay on to remind you which an issue has happened that should be check and investigated.

When you don’t know what’s wrong, an illuminated Check Engine Light can be annoying, and whether the problem is serious or just a small mistake. There’s no chance to understand what the issue is before you connected a scan tool into the vehicle’s diagnostic connector and looked over the code(s) that turned on the light.

If the engine appears to be running normally (no unusual smells, vibrations, noises, etc.) and there is no warning lights are on, you may assume the fault that’s triggering the Check Engine Light to come on is possibly minor and will not hinder what you can do to keep driving. However, if another warning lights are on, you’ll want to stop and look into the problem.

Malfunction Indicator Lamp
Malfunction Indicator Lamp
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When the Check Engine Light becomes on, there a record a DTC (diagnostic trouble code) within the PCM (power-train control module) memory which matches the fault. Specific issues could generate more than one trouble code, and many vehicles might have numerous issues that set multiple trouble codes.

In many vehicles that made before 1996 (older cars), disconnecting a battery cable or disconnecting the computer’s power source may remove fault codes, at least temporarily can turn off the Check Engine Light. When the problem continues, the code is going to reset, and the Check Engine Light will be back on. However, on several more recent vehicles, you don’t want to detach the battery because it can get rid of the computer’s memory settings. When it happens might impact the functioning of the climate control system, transmission, as well as other functions.

In newer vehicles (1996 up), to turn the Check Engine Light off and erase the codes you should use a scan tool or code reader.

Check Engine Light (Malfunction Indicator Lamp) On
Check Engine Light (Malfunction Indicator Lamp) On

How To Read Fault Codes Using A Scan Tool

Use a scan tool or code reader when your Check Engine light is on, to read the code(s). Connect the scan tool or code reader into the 16pin OBD diagnostic connector (commonly located on close to the steering column below the dash).

If the engine off (don’t start the engine yet), and the ignition key is turned on, the scan tool is going to communicate along with the PCM. You might need to type in the VIN code and model/make/year of your vehicle. And push the button that permits the scan tool by reading the codes or select on option “READ FAULT CODE” on the menu of code reader or scan tool. That what to do when the scan tool or code reader doesn’t automatically identify the application.

The scan tool will likely then show a code or number with the description that matches a specific fault code. For Power-train codes (which include all the vapor control system on the fuel tank, related emission, engine controls, controls, and catalytic converter) it’s named with letter “P.” In case there is a lot more than one code, the fault codes will likely be sort in numeric order.

Check Engine Light Important Notes

NOTE: Before you erase the displayed code, you should write the code(s) down on paper. You might need to recheck the codes when the same issue keeps coming back. Check Engine Light will turn off when you are erasing the codes, but at some time if the problem is still there, the codes will probably returning and triggering the Check Engine Light to turn on again.

Important: A fault code will show you which system or sensor that experienced some problem. However, the code won’t let you know why the fault happened, which part that needs to be to replaced how severe the failure is. That sometimes requires more enhanced diagnostics. For further assistance with specific fault codes, read the related articles on this website.

Diagnostics Of Check Engine Light

To OBD II prior, fault detection was mainly limited by “gross failures” within specific circuits or sensors. The initial generation systems weren’t with the capacity of detecting misfire, converter fuel or problems vapor leakages. OBD II changed all that by adding the capability to monitor these exact things so emission problems could be detected because they develop.

When a fault occurs, OBD II uses the Check Engine Light to alert the driver, and it will save the trouble codes that match with specific issues. When a problem occurs, it also captures a snapshot of sensor data and can track issues as they develop.

Almost every emission issue can cause the Check Engine Light on with OBD II if hydrocarbon emissions exceed 1.5 times the federal limit, even when there is no noticeable driveability issue accompanying the emission problem.

OBD II isn’t monitoring only the procedure of all engine’s systems (emissions, evaporative, EGR, ignition, fuel, etc.) and sensors. Besides, it also can identify engine misfires and monitors the operation of the catalytic converter. All issues may affect emissions can be monitored by OBD II, including a loose gas cap!

Understanding Diagnostic Trouble Codes

When the misfire occurs, it will cause the Check Engine Light to flash. The tool will set the code P030X when a misfire in a given cylinder occurs, misfiring cylinder marked as a number and can read on the “X” code. Example how to read it is when code P0301 appears on scan tool, and it means the cylinder number one is misfiring. Remember, the code that appears will not explain why the cylinder was misfiring. You should find out the cause of the problem by doing diagnostics and some tests. Misfire occurs due for some cause like worn cam lobe or leaky head gasket, leaky exhaust valve that causes loss of compression, dead or clogged fuel injector, on the DIS ignition system there is a defective ignition coil, a bad plug wire, fouled spark plug.

With the second oxygen sensor in the exhaust behind the converter, OBD II monitors the efficiency of the catalytic converter operation. How good the converter does its job can be done by comparing the readings of the current upstream and downstream O2 sensors. OBD II will turn the Check Engine Light on and set the code when there a drops the efficiency of the converter below a certain threshold.

Pulling a vacuum on the fuel system or fuel tank by pressurizing or evap plumbing, evaporative emissions (fuel vapor leaks) in the charcoal canister can be detected by OBD II. Losing or missing gas cap also can be recognized and will trigger the Check Engine Light on.

Another electronics problem also can generate OBD II codes, such as a compressor failure on air condition failures or various problem on electronic transmission.

Two Types Of Fault Codes

There two types of diagnostic trouble codes that generated by OBD II:
“Global” or “Generic,” code (P0) these are required by law and this for all makes and models of vehicles. “OEM” or “Enhanced,” code (P1) is for specific vehicles, and this code is unique. The enhanced codes will cover the failures and issues for non-emission that occurs outside the engine control system. Included is airbag codes and other body and electrical codes, ABS codes, HVAC codes.

Any basic scan tool or code reader can read and access the “generic” codes that are common to all vehicle manufacturers as long as the tools are compliant with OBD II. Older code reader or scan tools made before 1995 is not compliant with OBD II and won’t work on a new vehicle that made on 1996 up. To able doing diagnostic and read the OBD II codes, proper hardware and software are needed so that it can talk to old on-board computer vehicle. There no flash codes manual for newer cars made 1996 up, so the code reader or scan tools is required. In some exception, manual flash codes still provided by some Dodge and Nissan models. Most Toyota, Honda, Ford and GM models don’t provide flash codes manual. However, some GM models have a procedure to displayed codes manually on the driver information display.

Car Codes Reader Tools

On auto parts store, you can purchase a simple code reader under $60. Depend on the features, basic scan tools that can read codes, erase codes and additional system data can be purchased for $70-$400. Scan tools that have advanced features a usually used by professional technicians can cost several thousand dollars. This advanced scanning tool can run many self-tests that are built into the engine management system of your vehicle because it has bi-directional capabilities. If there any difficult-to-diagnose problems occurs this kind of advanced scan tools is required. Graph sensor voltages can be displayed on high-end professional level scan tools to reveal diagnostic data, where the simple/basic data can’t do that.

If you don’t have a code reader or scan device, take your vehicle to a repair shop or auto parts shop to diagnose the Check Engine Light problem.

TIP: You can get an FREE plug-in diagnosis on AutoZone or some another parts store, or if you want to do the basic diagnosis yourself in the parking a lot, they do a loan scan tools for you. Remember, the scan tool only show you the codes that turn Check Engine Light on and won’t tell you why it occurs and also will not tell you what parts should be replaced. You need to figure out that by your self and find the right solution.

Sample case, the scan tool read and display Random Misfire Code (P0300), the tool tell you if misfiring occurs in multiple cylinders and does not give you information the reason misfiring occurs. This misfiring can be due to several reasons, compression or ignition issues, or could be fuel issue or maybe all of above issue triggering the Check Engine Light turn on. You need to do some test to find out why misfiring occurs.

Check Engine Light On Then Your Vehicle Failed The Obd Plug-In Emissions Test

Any vehicle with Check Engine Light is on won’t pass the test of the OBD plug-in emissions. Make sure the Check Engine Light off and no codes in the PCM memory before you take the vehicle to the test. When original problem still there and unresolved, it’s useless to delete the code and take your vehicle to test station. Setting up the OBD II monitor take a time and sometimes it can take several days, and while in a set usually requires driving at various speeds. Completeness checks the self-test monitors performed by the OBD plug-in test is to give you the certainty of the feasibility of your vehicle, if the result is not ready, then your vehicle will be rejected.

The lamp of Check Engine Light is working properly or not also checked and determined by OBD plug-in test, if it has been disabled or burn out, you need to fix the problem first or replace the bulb, or your vehicle will be rejected.

The vehicle will fail the emissions test when the test finds any DTCs (Diagnostic Trouble Codes) codes. The list codes found and possible suggestions that were causing the fault should be printed by the test center. If you know how to do, have tools and can do yourself, as a suggestion you need to repair it. If you can’t do that, take the vehicle to the dealer and lets them fix the problem.