Automotive Diagnostic OBD2 Scanner

Even though it is hard to imagine that poor fuel economy can be a problem on these modern OBD II engines — with full management from the PCM (Powertrain Control Module), having continous self-adjusting parameters on the move, the reality is different.
If just one sensor fails, the system data can be tricked in thinking that the engine is lean on fuel. Therefore more fuel (richer fuel mixture) is sent through the injectors.

There are various fault factors that can all lead to this problem. When a standard (unmodified) OBD II system is working as designed the fuel efficiency is excellent, compared to traditional mechanical fuel injection or carburetters, as the PCM is constantly adjusting its parameters accordingly for optimum output, giving the least emissions output possible. The most common various causes are:

• Partially blocked air filter or restricted intake duct
• Defective fuel pressure regulator
• Leaky fuel injectors (might also be caused through gumming)
• Damaged fuel return pipe

These DTC (Data Trouble Codes) for the above problems can either be P0172 or P0175, or a combination of both (two TFCs listed on the diagnostic obd2 scanner/reader).

Bad mass airflow reading is another possible cause. The continuous flow of air inside the engine is constantly monitored and the PCM acts swiftly to these changes by changing the air to fuel ratio. This constant monitoring process is done through the (MAF) Mass Air Flow sensor. Possible problematic causes for the MAF sensor are:

• Loose MAF sensor plug connection
• Unplugged MAF sensor – usually forgotten after an engine service or some repairs
• MAF sensor plug contamination – either through corrosion (slightly difficult) or oil contamination after a service or through a leaky breather hose
• MAF sensor tip becomes dirty through polluted air — can be cleaned with auto factors sensor cleaner sprays or electronics cleaner
• MAF sensor has failed and must be replaced

The DTC for any of the above problems for the MAF sensor can range from code P0100 to P0104.

Some OBD II engines use an Inlet Air Temperature sensor (IAT) instead of the MAF sensor. This calculates the air temperature inside the inlet manifold through this sensor in along with the Throttle Position sensor(TPS) and MAP sensor. It the sensor is reading colder than it actually is, the fuel is automatically increased to compensate. Possible failure of the AIT sensor are:

• Bad AIT sensor plug connection (loose connection)
• Unplugged AIT sensor – usually forgotten after a service is done
• AIT sensor failure (least possible)

The DTC for any of the above problems for the AIT sensor can range from code P0070 to P0074

False manifold pressure readings can be another cause. This monitoring process is there to tell the PCM about the engine’s load and is done through the Manifold Absolute Pressure sensor (MAP). If the readings tells the PCM that the engine is under load it increases the fuel accordingly, so that it compensates for that particular engine load. The MAP sensor role is to calculate the manifold’s vacuum. Possible problems caused by the MAP sensor are:

• Loose or unplugged MAP sensor connector
• Vacuum leaks caused by perished vacuum hoses and /or loose vacuum pipe ends
• Blown manifold gaskets and / or seals

The DTC for any of the above problems for the MAF sensor can range from code P0105 to P0109.

The Engine Coolant Temperature sensor (ECT) may be another cause for such poor fuel economy. Usually this also has the tendency to put out excessive exhaust emissions when this sensor is not functioning. The monitoring purpose of this sensor is to tell the PCM the state of the engine’s temperature through the liquid coolant. If the sensor isn’t functioning and it’s readings tell the PCM that the engine is cold, the fuel mixture to air ratio is increased and the engine timing is advanced until the engine reaches its normal operating temperature. This can be like driving “on choke” in a carburettor engine when the engine warm. Emissions will usually be black in color. Possible causes for a faulty ECT sensor are:

• Leaking sensor seal which end up in the ECT sensor plug connector and build corrosion
• Faulty ECT sensor – will need immediate replacement

The DTC for any of the above problems for the ECT sensor can range from code P0115 to P0119.

Oxygen sensors (o2) can contribute to a poor fuel economy too. Oxygen sensors calculate the amount of unburnt fuel in the catalytic converter and adjust fuel mixture accordingly,giving the correct amount of ‘properly burnt’ exhaust emissions. If the O2 sensors are out of reading range they will normally indicate a lean mixture and so the PCM adds up on fuel mixture. The excessive fuel can easily damage the catalytic converter if left for any prolonged time. Possible causes for this fault are:

• Damaged O2 sensors
• Damaged O2 sensor heater
• Bad monitoring comparison between front and rear 02 sensors. This can also cause a bad DTC reading. For a more detailed info see article: Reference to OBD2 Sensors – Oxygen (O2) Sensors

The DTC for any of the above problems for the O2 sensor can range from code P0130 to P0167 and P0036 to P0064 for the O2 sensor heater.

Another excessive fuel wastage can be obtained from a misfiring engine. Misfiring can also cause other engine damages, like overheating between the walls of that particular cylinder, wears out engine mounts if left for any length of time due to the rough nature of the engine cycles, wear out exhaust flexible pipes, and even damage severely a catalytic converter. This usually happens because of raw fuel entering the catalyser which in turn ignite inside causing the catalytic to overheat and becomes red hot. This will end up ruining the catalytic converter.
Misfires causes can be:

• Contaminated spark plug/s or worn plug/s (not changed at recommended service intervals)
• Faulty HT (high Tension) spark plug wire (loose or damaged)
• Weak Distributor-less Ignition Coil (DIS) or Coil-on-Plug (COP) – depends on the factory design – needs replacement
• Clogged fuel injector (gummed up)
• Dead Fuel injector pulse – needs replacement

The DTC for any of the above problems for engine misfire is P030_ [where _ = number of misfiring cylinder] — eg. P0303

This is why all modern OBD II equipped engines must have all the above sensors working correctly. These sensors all contribute to less fuel wastage, strict controlled pollution within the legal parameters, and a longer engine service life. This is achieved through a much more controlled environment as opposed to the older engines. All mechanical uncontrolled variations are very limited compared to the older fully mechanical engines. There is no way to find out any of these faults accurately without using a diagnostic OBD2 scanner to tell what the fault is. Also without proper deep diagnosis the scantest can show other faults which may be “masked” by other faults, so just using a diagnostic OBD2 scanner or OBD II code reader for a faulty engine is not always enough. A true diagnosis by a qualified auto tech might be needed in certain cases.