Diagnosing Your Engine When There Are No Trouble Codes

Conducting an engine diagnostic when your vehicle's self-diagnostic system apparently isn't detecting any problems can be difficult. But you still can diagnose engine performance and driveability problems like...

• Loss of engine power
• No-crank condition
• Engine stalling issues
• Hard-start condition
• Increased fuel consumption
• Engine knock
• Backfire

...if you know what are the components or systems most likely to cause these common issues.

Since 1982, the On-Board Diagnostic (OBD) system has helped automotive technicians monitor and find problems with emission components or control systems that may have gone out of their normal operating parameters. A car's computer uses DTCs to pinpoint a potential system's fault.

Throughout the years, more emission related systems and components have been incorporated to the list of computer monitored systems.

Still, some performance and driveability problems can appear without the computer setting any DTC. So you need a different strategy to do a diagnostic without the help of a trouble code.

Each of the following sections describes a specific engine performance or driveability issue, followed by a brief explanation of the problem and the potential components and systems that might be involved in the issue. Also, each section is linked to a post related to the issue that goes into more detail. Thus, this linked post can guide you to diagnose and correct the problem.

Sometimes, a performance or driveability issue may show one or more symptoms. Paying attention to these symptoms will help you speed up your diagnostic.

So make a list of these symptoms, along with the conditions under which the problem appears. For example, you may notice that your engine stalls only when cold, after warming up, or intermittently. All this information can help you, or your mechanic, find the cause of the problem quicker, saving time and money.

Since this post is about diagnosing engine problems when there are no computer diagnostic codes, you may not see sensors or actuators in the following lists that otherwise may trigger the computer to set a DTC.

So head over to the section that best describes your car's performance or driveability issue to diagnose and make the necessary repairs.

Engine power loss can start in any of a number of components or systems. Whatever the cause, all have the same effect: your engine feels sluggish when you depress the gas pedal.

And trying to find the cause behind the problem can be frustrating. Here is a list of components and systems that can cause this problem:

Components:

• A failed MAF sensor
• Dirty air filter
• Throttle linkage problems
• Bad accelerator pedal position sensor
• Binding brake calipers

Systems:

• Ignition system
• Fuel delivery system
• Exhaust system
• Automatic transmission issues
• Variable camshaft timing system

For a systematic approach to diagnose the problem, head over to this post on causes for low engine power and some common troubleshooting procedures.

A no-crank condition happens when the starter motor itself fails to turn the crankshaft. Most of the time, the fault is in the starting system itself. If your check engine light hasn't come on, you may want to check the following:

Components:

• Starter motor
• Starter circuit
• Battery
• Starter relay or solenoid

Systems:

• Starting system
• Ignition system

This other post examines in more detail the causes of an engine that won't crank over. It has some simple tests to help you fix the problem.

Sometimes an engine may die for no apparent reason. The conditions under which it stalls can give you some clues about where the potential problem may be located. For example, the engine may stop running during idle or deceleration.

If your car's computer hasn't thrown any DTCs, you may want to check the following potential components or systems to find the fault.

Components:

• Loose fuel filler cap
• Clogging fuel filter
• Dirty or bad fuel injectors
• Faulty fuel pump

Systems:

• Fuel delivery problems
• Charging issues
• Intake air problems
• Automatic transmission problems

An engine can stall under different conditions, depending on the specific fault. For example, the engine may stall during acceleration, while idling, after reaching operating temperature, or stall intermittently. If you need more information or would like to conduct some tests at home, this other post on car stalling issues can help you.

There are a number of components and systems that can make it hard to start your engine, whether it's cold, warmed or both. Sometimes, finding the culprit can take a few minutes, hours, or much longer. But here is a list of the most common causes behind a hard-starting condition.

Components:

• Battery terminals (loose, corroded)
• Battery (charge state, electrical drain)
• Problem with a starter motor current draw
• Fuel pressure regulator fault
• Worn spark plugs
• No spark or weak spark
• Clogging fuel filter
• Bad engine grounds
• Vacuum leak
• Carbon buildup around valves
• Faulty MAF sensor

Systems:

• Starting system
• Fuel system
• Ignition system
• Exhaust system
• PCV system
• EVAP system

If you'd like to conduct some tests, check out this other post that can help you find the cause behind the hard-start condition of your vehicle.

Fuel consumption can go up because of a fault in a number of components or systems. Here is a list of those items you may want to check.

Component:

• Underinflated tires
• Fouled or worn spark plugs
• Failing or stuck open thermostat
• Leaking injectors
• Dirty MAF sensor
• Dragging brakes
• Transmission fluid level
• Automatic transmission problems

Systems:

• Bad ignition timing
• Ignition system problems
• Fuel system
• PCV system
• Exhaust system
• Intake air system
• Variable camshaft timing system

For more help to trace the problem, check this other post on fuel consumption issues.

Engine knock is a form of abnormal combustion where a secondary combustion process collides with a primary combustion process. On severe cases, detonation (strong knock) can blow a cylinder head gasket, cause damage to the combustion chamber or a valve. Problems with one or more of the following components or systems can upset the correct air/fuel ratio and lead to this condition.

Component:

• High engine temperature
• Aged or low coolant
• MAF sensor problems
• Cylinders carbon buildup

Systems:

• Secondary ignition system
• PCV system
• Fuel system
• Too advanced ignition timing

If you want to go into more detail about engine knock and diagnostic procedures, head over to this post on engine knock problems.

Backfires occur when fuel ignites in the intake or exhaust system. A backfire can be mild or strong, to the point of causing manifold damage. So try to diagnose and fix the problem as soon as possible. Here are some items and systems that may be behind a backfire.

Components:

• Clogging fuel filter
• Failed fuel pressure regulator
• Vacuum leak
• Exhaust leak
• Clogged or stuck closed EGR valve
• Valve train problems (failed to close valves)

Systems:

• Secondary ignition system
• Too retarded ignition timing
• Fuel system
• Exhaust system

For more help and other potential problems that may cause an engine to backfire, refer to this other post on engine backfires and some simple diagnostic procedures you can conduct at home.

Just because the check engine light (CEL) is not on it doesn't mean there are no codes in your computer memory. You car's computer may still store pending codes. These are codes related to potential problems the computer detected once and haven't reappeared. These codes can still help you. So scan the computer and see if there are any.

You can get more help from your vehicle repair manual for your specific vehicle make and model. If you don't have this manual yet, you can buy a relatively inexpensive, aftermarket Haynes manual with Amazon.

Haynes manuals come with a troubleshooting section and step-by-step procedures for many maintenance, repair and troubleshooting projects. So you can recuperate your small investment soon.