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Engine Trouble? Engine Diagnostic Experts D&R Automotive Explain

Published on
June 5, 2024

Engine diagnostics refers to the process of identifying issues with a vehicle's engine using specialized tools and analysis. At its core, engine diagnostics aims to pinpoint problems early, before they cause serious damage or performance problems. 

The key components involved in diagnostics include:

  • Engine Control Unit (ECU) - The ECU is the vehicle's main computer that oversees engine systems. It monitors data from sensors and controls components to ensure optimal performance.
  • On-Board Diagnostics (OBD) Port - The OBD port allows scan tools to access diagnostic information from the ECU. Technicians connect scan tools to pull diagnostic trouble codes (DTCs) that indicate issues.
  • Scan Tools - These handheld devices connect to the OBD port to read data from the ECU. They run tests and display information to aid diagnostics. Professional scan tools offer comprehensive capabilities.

Proper engine diagnostics are crucial for a few key reasons:

  • It enables early detection of minor issues before they become major. Identifying problems quickly reduces repair costs and prevents breakdowns.
  • Diagnostics allow technicians to zero in on the root cause of problems for proper repairs, rather than guessing. This avoids wasting time and money on unnecessary repairs.
  • Drivers can understand exactly what is wrong with the vehicle and the urgency of repairs. This facilitates informed repair decisions.
  • Diagnostics data guides preventative maintenance by revealing developing issues. This enables proactive service to maximize engine life.
  • Complete diagnostics ensure cars continue running safely and efficiently, providing driver confidence and peace of mind.

In summary, engine diagnostics leverage technology to provide vehicle insights critical for performance, reliability, and safety. Diagnostics keep both technicians and drivers well-informed.

Common Engine Issues

An engine is a complex machine with many moving parts, and there are a variety of issues that can arise. Here are some of the most common engine problems we see:


A misfire occurs when one or more cylinders fails to fire properly. This causes the engine to lose power and run roughly. Common causes include faulty spark plugs, bad ignition coils, damaged fuel injectors, vacuum leaks, or issues with the vehicle's computer. Symptoms of a misfire include reduced engine power, poor acceleration, rough idle, and the smell of unburnt fuel coming from the exhaust.

Oil Leaks  

Oil leaks are one of the most prevalent engine issues. The valve cover gasket, oil pan gasket, rear main seal, and crankshaft seal are all common sources of oil leaks. Oil leaks can be identified through oil spots on the ground, low oil levels, or smoke coming from the engine bay. Left unchecked, oil leaks can lead to insufficient oil and lubrication, resulting in severe engine damage. 


Engine overheating is very serious and should be addressed immediately to avoid catastrophic failure. Common causes include low coolant levels, faulty radiator fan, broken thermostat, blocked radiator, water pump failure, and blown head gasket. Symptoms include high engine temperature gauge reading, steaming or leaking coolant, sweet-smelling exhaust, and warning lights.

Oxygen Sensor Failure 

The oxygen sensor monitors the air-fuel ratio and reports to the computer. When it fails, it provides inaccurate readings that cause performance issues, reduced fuel economy, and an illuminated check engine light. Failed oxygen sensors need to be replaced to restore engine performance.

By being aware of the most common engine problems, their causes, and symptoms, you can address issues promptly to avoid further damage and expense. Our expert technicians have extensive experience diagnosing and repairing all types of engine issues. Please contact us if you suspect your vehicle may have an engine problem.

The Check Engine Light

The check engine light, also known as the malfunction indicator lamp, is a critical component of a vehicle's on-board diagnostics (OBD) system. This amber or yellow warning light serves an important purpose - alerting the driver of issues detected within the vehicle's emissions, engine, or transmission systems. 

When the check engine light illuminates, it means the vehicle's OBD system has detected a problem. This is often triggered by a fault code stored in the system when parameters fall outside of normal ranges. Some common causes include:

  • Oxygen sensor failure
  • Loose or faulty gas cap 
  • Ignition system malfunction 
  • Failed mass air flow sensor
  • Defective catalytic converter
  • Faulty spark plugs or wires

The severity of the detected issue determines if the light stays steady or flashes. A steady check engine light indicates a minor problem, while a flashing light signals a more urgent issue. Drivers should not ignore this warning sign, as continuing to operate the vehicle could lead to further damage or part failure. It's important to diagnose the cause through an OBD scan tool.

While the check engine light is not an emergency alert, it provides vital information to prevent small issues from escalating. Understanding the purpose and meaning of this lamp helps drivers remain attentive to their vehicle's health. Diagnosing problems early is the key to avoiding breakdowns and costly repairs down the road.

One way to diagnose engine issues is to review the onboard diagnostics system. So let’s take a look at what that looks like.

OBD Codes

One of the most important tools for engine diagnostics is the onboard diagnostics (OBD) system. All cars and light trucks built and sold in the US after 1996 have an OBD system that monitors emissions controls and key engine components. 

The OBD system uses sensors placed throughout the engine and chassis to monitor operations. If a problem is detected, the system turns on the check engine light and stores a diagnostic trouble code (DTC), commonly referred to as an OBD code. 

Our mechanics use these OBD codes to understand what's going on under the hood. The codes provide information on the part of the engine where the issue was detected. OBD codes consist of a letter followed by four numbers, such as P0301. The letter(s) indicate the type of code and the numbers provide more detailed information on the specific issue.

Here are some common OBD codes and what they mean:

  • P0301 - Misfire in cylinder 1 
  • P0302 - Misfire in cylinder 2
  • P0303 - Misfire in cylinder 3 
  • P0304 - Misfire in cylinder 4
  • P0300 - Random multiple cylinder misfire
  • P0420 - Catalytic converter issue 
  • P0430 - Catalytic converter issue
  • P0171 - System too lean
  • P0174 - System too rich
  • P0455 - Evaporative emissions system leak

By decoding the OBD codes, our mechanics can better pinpoint the root cause of engine issues. This allows them to more efficiently troubleshoot problems and make necessary repairs.

Engine Diagnostic Process

Our professional mechanics use a systematic approach when diagnosing engine issues. The process involves gathering information, testing components, and isolating the root cause.

The first step is to visually inspect the engine compartment for any obvious issues like leaks, damaged wires, or loose connections. Our mechanics will also review the vehicle's maintenance history and scan for any diagnostic trouble codes using a specialized scan tool connected to the onboard diagnostics (OBD) port. 

Next, our mechanic will conduct a series of tests to further pinpoint the issue. This may involve checking engine compression, performing cylinder balance tests, testing ignition coils, measuring fuel pressure, verifying sensor readings, and more. The tests allow the mechanic to compare readings across similar components to identify abnormalities.

If initial tests prove inconclusive, more advanced diagnostics may be required. This can include live data graphing, EVAP system smoke testing, simulated sensor inputs, and actuating components to analyze system reactions. The mechanic methodically isolates circuits and components to zone in on the root cause.

Patience and persistence are required, as some intermittent or complex issues take time to resolve. But with the right diagnostic process, our mechanics can accurately determine the underlying problem and recommend the appropriate repair.

Engine Sensors 

Modern vehicles contain a variety of sensors that monitor the engine system and allow it to operate efficiently. These sensors track key data parameters and communicate with the vehicle's computer, known as the Engine Control Module (ECM). Some common engine sensors include:

Oxygen Sensors - Also called O2 sensors, these measure the oxygen levels in the exhaust system. They help determine if the fuel mixture going into the engine is rich or lean. Faulty O2 sensors can cause poor fuel economy, engine misfires, and problems with emissions.

Mass Airflow Sensor - This sensor calculates the volume and density of air entering the engine. The computer uses this input to calculate the optimal fuel ratio. Mass airflow sensor problems can lead to a rough idle, stalling, power loss, and poor acceleration.

Crankshaft Position Sensor - This sensor monitors the rotational speed and position of the crankshaft. It provides vital data for ignition and fuel injection timing. Failure of this sensor may prevent the engine from starting or cause it to stall while running.  

Camshaft Position Sensor - The camshaft sensor determines which pistons are in the power stroke and sends this info to the computer. This allows the computer to synchronize fuel injection and ignition timing. Issues with this sensor can affect engine performance and idle quality.

Coolant Temperature Sensor - As its name implies, this sensor measures the temperature of the coolant and communicates it to the ECM. The computer uses this data to adjust the fuel mixture and engine functions for optimal performance during cold starts and warm-up periods. A bad coolant temperature sensor can cause a rough idle, poor fuel economy, and drivability problems.

Throttle Position Sensor - The throttle position sensor monitors the throttle valve position and reports it to the computer. This helps regulate air intake and fuel flow at different throttle openings. Defective throttle position sensors can lead to acceleration issues, stalling, rough idle, and hesitation.

Paying attention to any error codes related to engine sensors and addressing problems promptly is key to avoiding more serious issues down the line. Consult a professional technician for diagnosing and replacing any faulty engine sensors.

Engine Troubleshooting Tips

When your check engine light comes on, it can be concerning but there are some simple troubleshooting steps you can try yourself before taking your vehicle to a professional:

  • Check your gas cap - A loose or damaged gas cap can cause the check engine light to illuminate. Make sure the cap is tightened properly and inspect it for any cracks or damage. Tighten the cap and drive for a few days to see if the light turns off.
  • Check your oxygen sensors - The oxygen sensors monitor the air-fuel ratio going into the engine. If they get contaminated or stop functioning properly, it will trigger the check engine light. If you know how, inspect the oxygen sensor wiring for any damage.
  • Replace the air filter - A dirty air filter can restrict airflow to the engine, potentially leading to the check engine light coming on. Replacing the air filter can help restore proper airflow.
  • Inspect spark plugs and wires - Faulty spark plugs and worn spark plug wires can cause misfires in the engine, triggering the check engine light. Check for any corrosion or damage.
  • Monitor fluid levels - Low oil, coolant, or transmission fluid can cause engine issues and lead to the check engine light turning on. Top up any low fluids and maintain proper levels. 

If the check engine light persists after basic troubleshooting, it's best to have your vehicle professionally diagnosed by us here in Jonesboro, AR. Our mechanic can use computerized diagnostic tools to read engine codes and pinpoint the exact cause. Some issues that require a professional assessment include:

  • Faulty oxygen sensor 
  • Problems with the mass airflow sensor
  • Issues with the catalytic converter
  • Faulty ignition coils 
  • Leaks causing low fluid levels
  • Damaged spark plugs/wires
  • Engine misfires 

Don't ignore the check engine light for an extended period, as it could lead to further engine damage. Schedule an engine diagnostic inspection as soon as possible if DIY fixes don't solve the issue. Our expert technicians have the skills and tools to accurately diagnose any check engine light causes.

D&R Automotive Engine Diagnostic Service

At D&R automotive in Jonesboro, AR, we offer a full range of engine diagnostic services to accurately detect and resolve engine issues in all makes and models. Our expert ASE certified technicians have years of hands-on experience troubleshooting engine problems and getting to the root cause. We utilize industry-leading diagnostic tools and equipment to efficiently diagnose your vehicle.

Our engine diagnostic process is very thorough and includes these key steps:

  • On-board computer scan - We connect specialized scanners to read any diagnostic trouble codes that pinpoint problems. This gives us a starting point.
  • Visual inspection - We thoroughly inspect the engine bay looking for leaks, damage, loose parts, etc. 
  • Sensor testing - Engine sensors are tested to ensure proper operation. Common sensors checked include O2, MAP, crankshaft position, camshaft position, and more. 
  • Performance testing - The engine may be put under load on a dynamometer to check performance, emissions, and identify issues.
  • Leak down/compression test - These tests check for internal engine problems like worn piston rings or valves. 
  • Additional testing as needed - Based on initial findings, we conduct further testing like fuel pressure, electrical system diagnosis, etc.

Our technicians utilize industry-leading scan tools, lab scopes, pressure transducers, and other high-tech equipment for precise diagnostics. We invest heavily in the latest technology to efficiently solve your vehicle's issues.

With our expertise and advanced tools, we can quickly and accurately diagnose any engine performance problems and get your vehicle running great again. Contact us today to schedule engine diagnostic services and resolve that check engine light!

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