Checking the causes of diesel engine malfunctions (Skoda Kodiaq NS7)

Contents: Checking the root causes of…⬇ Checking for additional causes of…⬇

Note:

Make sure the following conditions are met:

The Engine Control Module (ECM) and Malfunction Indicator Lamp (MIL) are functioning properly.

There are no diagnostic trouble codes (DTCs) stored in memory.

The diagnostic tool data is within the normal operating range.

The fuel system has no leaks.

The air filter element has no limitations.

The vehicle's tires are inflated to the proper air pressure and meet original equipment specifications.

Checking the root causes of malfunctions

1. Check the following conditions of the sensor systems:

Check the mass air flow (MAF) sensor for blockages, contamination, or damage.
Test for an intermittent fuel rail pressure sensor signal by wiggling the harness connector between the fuel rail pressure sensor and the ECM with the ignition on and the engine off while monitoring the appropriate parameter with a scan tool.
Check if the crankshaft position sensor signal is intermittent.
Check if the crankshaft position sensor resistance is within the acceptable range. After the fuel has evaporated on a hot engine, the resistance of the crankshaft position sensor may go outside the acceptable range. The resistance should be in the range of 774-946 Q.
Check the engine coolant temperature (ECT) sensor. Use a scan tool to compare ECT data with the intake air temperature (IAT) sensor data when the engine is cold. The IAT and ECT intake air temperature readings should differ by no more than 3°C (5°F). If this is not the case, check the coolant sensor circuit or the sensor itself for excessive resistance.

2. Check the following fuel system conditions:

Check for external fuel leaks.
Check if the fuel pressure is too low.
Make sure the fuel filter is not clogged and that no air has entered the fuel system.
Check the fuel supply to the high-pressure fuel pump (HPFP).
Check that the hole in the fuel tank cap is functioning properly.
Check the quality of the fuel.
With the engine idling, monitor the actual and desired fuel rail pressure using a diagnostic tool.
If the ECM or fuel injector has recently been replaced, the fuel injector flow values may need to be confirmed.
Make sure the fuel injectors are not clogged or restricted.
Check if the fuel pressure regulator is sticking. A symptom of this malfunction may be an idle surge of at least 100 rpm. The surge may be at least 50 rpm above the desired idle speed and 50 rpm below the desired idle speed.

3. Make sure that the engine does not have the following mechanical damage:

The valve control mechanism is not working properly.
The valve rocker arm is worn out.
Low compression ratio in the engine.
Valve springs are broken or weak.
Worn camshaft lobes.
Excessive amount of oil in the combustion chamber. Valve seal leakage.

Note: If the problem persists after checking the above symptoms, you should check for additional causes of the problem.

Checking for additional causes of malfunctions

Hard start

Make sure the ECT value is within the specified range.
Check if the startup is too slow.
Make sure the engine electrical system is working properly.
Make sure the driver uses the correct starting procedure as described in the vehicle owner's manual.
Check for restrictions in the turbocharger intake manifold.
Check for restrictions or leaks in the intake manifold.
Check for restrictions in the exhaust system.
Check if the crankshaft axial runout is too large: in this case, the alignment of the magnetic wheel of the crankshaft position sensor and the crankshaft position sensor itself may be disrupted.

Interruptions, short-term "gaps", "twitching"

Check the generator.
Check if the crankshaft axial runout is too large: in this case, the alignment of the magnetic wheel of the crankshaft position sensor and the crankshaft position sensor itself may be disrupted.

High fuel consumption

The vehicle was carrying a heavy load or was being towed.
Too often, very strong accelerations were carried out.
Check for brake drag.
Check that the air pressure in your tires is correct.
Check that the speedometer is working correctly.
Check for air leaks in the charge air cooler.
Check that the air conditioning system is functioning properly.
Make sure the ECT value is within the specified range.

Hesitation and misfires, lack of power or intermittent stops

Make sure the engine electrical system is working properly.
Compare the vehicle with a similar module. Make sure the car is in real condition.
Check if the gearbox is working properly.
Check the level and quality of engine oil.
Check for air leaks in the charge air cooler.
Check the turbocharger turbine wheel, shaft and compressor impeller for wear or damage.
Make sure the exhaust passages are not clogged or restricted.
Check for restrictions in the charge air cooler.
Check if the mass air flow sensor readings are offset.
Make sure the exhaust gas recirculation (EGR) valve closes completely.
Before manually changing the position of the exhaust gas recirculation (EGR) valve, make sure it is not sticking.
Check the operation of the torque converter clutch.
Check that the air conditioning system is functioning properly.

Rough, unstable or incorrect idle, engine stalls

Check the engine mounts.
Check for casting defects in the intake and exhaust manifolds.
Check that the exhaust pipes are not damaged or pinched.
Check that the inner walls of the exhaust manifold are not damaged.
The mufflers failed due to exposure to high temperatures or a possible internal defect.
Check the park/neutral position switch circuit.

Material is available on the website [SKODABOOK]

Jerks, splashes

Make sure the driver understands how the torque converter clutch (TCC) operates.
Make sure the driver understands how the air conditioning compressor works.
Use a scan tool to ensure the vehicle speed sensor (VSS) reading matches the speedometer reading.

Fuel system knocking/combustion system noise

Check for obvious overheating issues.
Make sure the engine coolant level is high enough.
Make sure there are no restrictions on air flow through the radiator.
Check the correct functioning and type of thermostat.
Check the coolant solution. This solution should consist of antifreeze and water in a 50/50 ratio.

Increased smoke (black smoke)

Normal mode

There should be no black smoke during light to moderate acceleration.
With 2-3 sharp accelerations performed after normal minor acceleration, a short-term emission of black smoke is possible, lasting no more than 5 seconds.
During sharp acceleration, the appearance of a very small amount of black smoke is allowed.

Abnormal mode

Black smoke during light to moderate acceleration.
Emission of thick black smoke during sudden acceleration, lasting for more than 5 seconds.
Thick black smoke with every sharp acceleration and/or during gear changes.
Check for air leaks in the charge air cooler or in the air ducts between the turbocharger and the intake manifold.
Check for obstructions to the air flow in the turbocharger charge air cooler.
Check that there are no obstructions to the air flow in the intake manifold.
Check that the EGR valve closes completely. Remove the EGR valve and visually inspect it for any gaps between the valves and valve seats.
Before manually changing the position of the exhaust gas recirculation (EGR) valve, make sure it is not sticking.
Check that too much oil is not entering the combustion chamber.

Increased smoke (white or gray smoke)

Check the coolant level in the reservoir. White smoke associated with coolant may be mistaken for blue or gray smoke. If the coolant level is low, check the cooling system for leaks.
If there is excessive smoke, check to see if any fuel injectors are stuck open by doing the following:

1. Disconnect the electrical connector on the high pressure fuel pump.

2. Remove the glow plugs.

Note: Do not stand in front of the glow plug holes while cranking the engine.

3. While cranking the engine, you should simultaneously observe the fuel spray through the holes intended for the glow plugs.

4. Replace the fuel injectors of the cylinders in which the fuel is sprayed.

5. Check the cleanliness of the oil and make sure that its level is not elevated.