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How to Check the Engine in Vehicles

by Contributing Writer; Updated June 12, 2017

An On-Board Diagnostic scanner can help check a Vehicles engine. The service engine soon light does not need to be lit. The diagnostic system routinely monitors the engine Vehicles problems, and when a malfunction is sensed, the service light becomes active and a trouble code is issued. The Vehicles computer system, however, does not class every problem as trouble code worthy. The problem has to repeat itself a number of times. In the meantime, the system classes these faults as "pending. " Retrieving pending codes is just as easy as pulling trouble codes.

Under The Hood:

 How to Check the Engine in an Infiniti G35

Connect a diagnostic cable to your OBD-II scanner, and then connect the cable to the Infinit G35's computer outlet. This port is commonly referred to as a Data Link Connector, and it can be found underneath the Infiniti's dash, near the hood release. It will not be covered, and you need no tools access it.

Turn the Infiniti G35's ignition key to the "On" position. Some diagnostic handhelds require not just the electronic system to be active, but the Infiniti's engine running.

Retrieve the codes by pressing the appropriate command buttons. OBD-II code readers and scanners all have different physical layouts with buttons located in different places. You will need to consult your handheld's user manual for the exact, appropriate procedure. If you own a preset scanner that automatically pulls OBD-II codes upon connection, then you need not worry about any of this.

Look at the codes on your screen. For the time being, you only need to be concerned with OBD-II codes that start with the letter "P." Those are powertrain codes. Also, look at how the your device distinguishes the codes. There should be an icon or some other indicator for "trouble" and "pending" code status.

Find the definitions and explanations for the OBD-II codes on your screen. Your Infiniti G35 will not have these within its pages. Generic OBD-II codes are used on all OBD-II compliant vehicles, and these will more than likely be found in your scanner's manual. If you cannot find them there, you can easily locate OBD-II codes online. Infiniti has a separate set of codes unique to their vehicles. Those are also not in your vehicle's manual, but they will likely not be in your scanner's manual. You will need to find this online, as well.

Compile a list of problems suggested by your Infiniti's computer, based on the coding definitions. Read over this list and consider your own level of expertise and experience. You are confident in your ability, open the Infiniti's hood and troubleshoot the engine in further detail. If the problems are beyond your capabilities, seriously consider driving the G35 to a repair shop.

Items you will need

  • OBD-II scanner

 How to Check the Engine in My Nissan Quest Van

Plug an OBD II scanner onto your OBD II port, which located underneath the steering wheel on a panel containing a trapezoidal-shaped connection that fits into the OBD II scanner's input. If the Nissan Quest is signaling the check engine light, then the OBD II scanner will tell you what problems the vehicle's computer system is sensing. The code may indicate a component is not working, such as a sensor. However, it will not tell you whether it is the sensor itself that has failed or if it is the wiring that is part of the electrical system which connects with the sensor.

Check the engine fluids, starting with the coolant, which should be done while the engine is still cold. Open the radiator cap to check the fluid level and look at the fluid reservoir to see if the fluid is between the maximum and minimum lines. Add more fluid if the coolant is low. Low coolant levels, which inevitably accompany coolant leaks, are dangerous to your Quest as it could lead to overheating and permanent engine failure. Coolant leaks look like a rainbow-oily substance found beneath your van.

Remove the oil dipstick in order to check the oil level. Wipe the dipstick clean with a rag and reinsert it into the dipstick tube. Remove the dipstick again and inspect the oil level by looking at the max and min lines printed on the dipstick. Add more oil by pouring it through a funnel placed in the oil cap of the valve cover. Always check the oil again once you have added oil to the engine to make sure that it is at the correct level.

Inspect the engine for oil leaks, which are indicated by pools of oil beneath the vehicle as well as carbon deposits and buildup around the gaskets where the oil is circulated. One of the more common leaks usually starts with the front valve cover. If you have a leak, unbolt the front valve cover and use a screwdriver to remove the old gasket. Insert the new gasket and bolt it back on to the lower valve cover.

Check the tension on the drive belts by depressing them in the center of the belt, exactly between two pulleys. The belt should deflect 1/4 inch if the belt distance is 7-11 inches between pulleys. The belt should deflect up to 1/2 inch if the distance between pulleys is 12-16 inches. If the belts are too loose, tighten them by turning the adjustment bolt with a socket wrench.

Items you will need

  • OBD II scanner

  • Engine oil

  • Funnels

  • Gasket replacement kit

  • Screwdriver

  • Antifreeze mixture (50 / 50)

  • Socket wrench

  • Wrench set

 How to Check the Engine in an Elantra

Consult your scanner's user manual for trouble code definitions. Mark the page the list begins, and set it on top of your Elantra's dashboard.

Insert the Elantra's key into the ignition, but leave the engine and the electrical system off.

Locate the Elantra's data link connector below the dashboard. It will be uncovered and to the left of the steering column. Plug your OBD-II scanner into this outlet. What to do next will depend on the exact OBD-II scanner you have purchased. The process is fundamentally similar across brands, but there are variations and differing button configurations. CarMD's scanner, for example, does not require you to start your engine, but others like Actron's CP9125 does.

Start the Elantra's engine if your scanner calls for it. Also, some scanners will activate themselves once a connection is sensed with a diagnostic scanner. Some scanners have to be manually switched on.

Look at the trouble codes displayed on your screen. Scroll through these and look for codes that are "pending."

Consult the manual you left on the dashboard for code descriptions. OBD-II codes are divided into two general classes. There are generic codes universal to all vehicles OBD-II compliant vehicles. There are also codes that are particular to Hyundai vehicles. If you manual does not contain these codes, you will have to go online and find the codes at a non-Hyundai related website. If your scanner's manual does not contain the codes at all, it may be because it comes with a software package that needs to be installed on your home computer. These type of programs are meant to assist in vehicle diagnostics.

Turn the car off and disconnect the scanner from the data link connection. Use the code definitions to troubleshoot the engine. If the problems sound more advanced then your experience or skill level, consider driving the Elantra to a Hyundai approved mechanic.

Items you will need

  • OBD-II scanner

 How to Check the Engine of a Mercedes Benz

Locate the diagnostic port on your Mercedes. This data link connection is the gateway into the Mercedes' computer. Location may vary by model. In the 2009 M Class vehicles, for example, it is covered and is located near the hood release. The connection is not covered in 2009 E Class vehicles, but is in a similar location. If you experience any confusion finding the outlet, there is a locator online that can help.

Connect your diagnostic scanner to the Mercedes data link connection. The procedure will vary by the brand and type of scanner you own. Consult your scanner's manual for the precise steps.

Either turn the Mercedes' electrical system on or start the engine, whichever the instruction for your scanner specify. If your scanner is not the type that self activates, you will need to press the power button and key in the "read" or "scan" commands.

Read the codes that appear on the scanner. If your "service engine" light on your dashboard is on, you will see trouble codes. Those should be addressed immediately. If you scroll through the codes, you can find codes that are classed as "pending." These are the codes that can help you troubleshoot an engine, if the service light is inactive.

Read through your scanner's manual for code meanings. There should be a list of them, usually in an appendix. The scanner's manual may only have generic codes used in all vehicles. Mercedes has supplemental codes that can be found online.

Items you will need

  • OBD-II or EOBD diagnostic scanner

About the Author

This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information. To submit your questions or ideas, or to simply learn more about It Still Runs, contact us.

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