أوضاع الخدمة في OBD-II

Live sensor and calculated values, read while the engine runs. This is where diagnosis actually happens — a stored code tells you what the module concluded, but Mode 01 lets you watch the inputs it concluded it from. The great majority of a technician's scan-tool time is spent here.

• 00 Supported PIDs 01–20 A bitmask telling the scan tool which of PIDs 01 to 20 this vehicle actually supports. Scan tools query this first, which is why two vehicles show different parameter lists. Engine Management and Sensors
• 01 Monitor status since codes cleared Warning lamp state, the number of stored codes, and which readiness monitors have completed. This is the parameter an emissions test reads to decide whether the vehicle is even testable. Engine Management and Sensors
• 03 Fuel system status Whether fuelling is running open-loop or closed-loop, per bank. Open loop means the module is ignoring the oxygen sensors and using a fixed map — expected when cold, a fault when warm. Fuel Delivery
• 04 Calculated engine load Current airflow as a proportion of peak available airflow. The single most useful parameter for judging whether other readings make sense — a fuel trim figure means nothing without knowing the load it was measured at. Engine Management and Sensors 0–100 %
• 05 Engine coolant temperature Coolant temperature as the control module sees it. Check this against ambient at a genuine cold start: if it disagrees with intake air temperature after standing overnight, the sensor is drifting. Cooling -40 – 215 °C
• 06 Short term fuel trim — Bank 1 The module's immediate fuelling correction, moving constantly as the oxygen sensor switches. Positive means it is adding fuel to correct a lean condition. Read alongside long term trim — short term swinging while long term sits high tells a different story from both being high. Fuel Delivery -100 – 99.2 %
• 07 Long term fuel trim — Bank 1 The learned, persistent correction the module has settled on. This is the parameter behind P0171 and P0172, and the one worth comparing at idle versus higher load: a vacuum leak drives it strongly positive at idle and less so under load, while a fuel delivery problem does the reverse. Fuel Delivery -100 – 99.2 %
• 08 Short term fuel trim — Bank 2 Bank 2's immediate correction. Comparing the two banks is the fastest way to separate a bank-specific fault from a shared one. Fuel Delivery -100 – 99.2 %
• 09 Long term fuel trim — Bank 2 Bank 2's learned correction. Both banks drifting together points at the airflow sensor, fuel pressure or the evaporative system; one bank alone points at that bank's injectors, gasket or sensor. Fuel Delivery -100 – 99.2 %
• 0A Fuel pressure Gauge fuel pressure, where a sensor is fitted. Coarse resolution compared with the dedicated rail pressure PIDs, and absent on many vehicles. Fuel Delivery 0–765 kPa
• 0B Intake manifold absolute pressure Absolute manifold pressure — high at idle means poor vacuum, which points at a large leak, a restricted exhaust or worn valve timing. With the engine off it should read local atmospheric pressure, which is a free sanity check on the sensor. Air Intake and Metering 0–255 kPa
• 0C Engine speed Engine speed, derived from the crankshaft position signal. An erratic or dropping value with the engine running steadily is strong evidence of a crankshaft sensor or reluctor problem rather than anything to do with fuelling. Engine Management and Sensors 0–16383.75 rpm
• 0D Vehicle speed Road speed as the module sees it. Compare with an independent reference: incorrect wheel or tyre sizes shift this calibration and can produce plausible but wrong readings with no component fault. Vehicle and Chassis Sensors 0–255 km/h
• 0E Timing advance Ignition timing relative to top dead centre. Persistently retarded timing under load, with no other obvious fault, points at the knock control system pulling advance — either genuine detonation or a knock sensor reporting noise that is not. Ignition -64 – 63.5 °
• 0F Intake air temperature Temperature of air entering the engine. On a forced-induction vehicle, watch this rise under sustained load: a large climb indicates the intercooler is not doing its job, which costs power and raises detonation risk. Air Intake and Metering -40 – 215 °C
• 10 Mass air flow rate Measured air mass entering the engine. A rough field check: at wide-open throttle a healthy naturally aspirated engine flows roughly its displacement in litres times its speed in thousands of rpm, in grams per second. Well below that suggests a restriction or a lazy sensor. Air Intake and Metering 0–655.35 g/s
• 11 Throttle position Throttle plate position. Sweep the pedal slowly and watch for a flat step in an otherwise smooth rise — that dead spot is a worn sensor track, and it is invisible to any static measurement. Air Intake and Metering 0–100 %
• 1C OBD standards conformance Which OBD standard the vehicle conforms to. Determines which modes and monitors to expect, and explains why some parameters are simply absent on a given vehicle. Engine Management and Sensors
• 1F Run time since engine start Seconds since the engine started. Useful context for freeze frame data — a fault stored three seconds after startup means something quite different from one stored after forty minutes. Engine Management and Sensors 0–65535 s
• 21 Distance travelled with warning lamp on How far the vehicle has been driven with the warning lamp illuminated. Honest history: it reveals whether a fault is new or has been ignored for months, which matters when judging secondary damage. Engine Management and Sensors 0–65535 km
• 22 Fuel rail pressure relative to manifold Rail pressure measured relative to manifold vacuum, which is what actually determines injector flow. More diagnostically meaningful than absolute pressure on port-injected engines. Fuel Delivery 0–5177.27 kPa
• 23 Fuel rail gauge pressure Rail pressure for direct injection and diesel systems, where pressures run far higher. Compare commanded against actual across the load range — that comparison is the core of diagnosing P0087 and P0088. Fuel Delivery 0–655350 kPa
• 2C Commanded EGR How much exhaust gas recirculation the module is asking for. Compare with EGR error to see whether the valve is complying — a commanded value with a large error means the valve is stuck, usually with soot. Exhaust and Emissions 0–100 %
• 2D EGR error Difference between commanded and actual EGR position. Large sustained error is the signature of a carboned-up valve, which is among the most common diesel faults there is. Exhaust and Emissions -100 – 99.2 %
• 2E Commanded evaporative purge How much stored fuel vapour the module is drawing from the charcoal canister. A purge valve stuck open dumps vapour continuously and produces a rich condition that looks like a fuelling fault. Exhaust and Emissions 0–100 %
• 2F Fuel tank level input Fuel level as a percentage. More than a gauge reading — several monitors are inhibited when the tank is very low or very full, which is why some faults will not reproduce until the level is right. Fuel Delivery 0–100 %
• 30 Warm-ups since codes cleared Completed warm-up cycles since the last clear. Together with distance since cleared, this reveals whether codes were erased recently — including immediately before an emissions test. Engine Management and Sensors 0–255 count
• 31 Distance since codes cleared Distance driven since codes were last erased. A very low value on a vehicle presented for sale or test is worth noticing. Engine Management and Sensors 0–65535 km
• 33 Absolute barometric pressure Atmospheric pressure, used for altitude correction. Should closely match manifold pressure with the engine off — a disagreement there is the basis of the P0069 correlation check. Engine Management and Sensors 0–255 kPa
• 3C Catalyst temperature — Bank 1 Sensor 1 Catalytic converter temperature. Runs hot when the converter is working, and runs alarmingly hot when unburnt fuel from a misfire is being burnt inside it — which is precisely the damage a flashing warning lamp is warning about. Exhaust and Emissions -40 – 6513.5 °C
• 41 Monitor status this drive cycle Which monitors have run during the current drive cycle. Useful when trying to complete readiness for an emissions test — it shows what is still outstanding rather than leaving you to guess at the drive cycle. Engine Management and Sensors
• 42 Control module voltage Supply voltage at the control module. Worth checking early in any confusing diagnosis: low or unstable voltage produces sensor readings that look like component faults, and chasing those wastes hours. Electrical and Charging 0–65.54 V
• 43 Absolute load value Load normalised against a fixed reference rather than current conditions, which makes it comparable across vehicles and useful for judging whether an engine is producing what it should. Engine Management and Sensors 0–25700 %
• 44 Commanded air-fuel equivalence ratio Target mixture expressed as lambda, where 1.0 is stoichiometric. Reading the target alongside what the wideband sensor actually reports is how you tell a fuelling problem from a sensor problem. Fuel Delivery 0–2 λ
• 45 Relative throttle position Throttle position relative to its learned closed position. Diverging from absolute throttle position indicates the learned closed point has drifted — common after cleaning a throttle body without performing the relearn. Air Intake and Metering 0–100 %
• 46 Ambient air temperature Outside air temperature. Compare against intake air temperature at a cold start — they should agree closely, and a persistent offset identifies which of the two has drifted. Vehicle and Chassis Sensors -40 – 215 °C
• 47 Absolute throttle position B The second throttle position sensor. Its whole purpose is cross-checking the first, so watching both through a pedal sweep is how the P0220-series correlation faults are actually found. Air Intake and Metering 0–100 %
• 49 Accelerator pedal position D Pedal position from the first pedal sensor. Distinct from throttle position — comparing pedal demand against throttle response separates a driver-input fault from a throttle actuator fault. Engine Management and Sensors 0–100 %
• 4A Accelerator pedal position E The second pedal sensor, on a different voltage slope from the first so that no single failure can misrepresent driver intent. Engine Management and Sensors 0–100 %
• 4C Commanded throttle actuator What the module is telling the throttle to do. Commanded opening with no matching actual opening means the plate is binding or the actuator has failed — a distinction no code makes for you. Air Intake and Metering 0–100 %
• 4D Time run with warning lamp on Minutes of engine running with the warning lamp illuminated. Alongside distance with the lamp on, this establishes how long a fault has been tolerated. Engine Management and Sensors 0–65535 min
• 4E Time since codes cleared Minutes of running since codes were erased. Engine Management and Sensors 0–65535 min
• 51 Fuel type Declared fuel type. Worth confirming on flexible-fuel and dual-fuel vehicles, since it changes which monitors run and what mixture targets apply. Fuel Delivery
• 52 Ethanol fuel percentage Measured ethanol content. A value that never changes after refuelling with a different blend indicates the composition sensor has stopped responding. Fuel Delivery 0–100 %
• 59 Fuel rail absolute pressure Absolute rail pressure on high-pressure systems. The parameter to watch when diagnosing the P0087 to P0094 group, and the one to compare against an independent gauge when a drifting sensor is suspected. Fuel Delivery 0–655350 kPa
• 5A Relative accelerator pedal position Pedal position relative to its learned rest point. Engine Management and Sensors 0–100 %
• 5B Hybrid battery pack remaining life Remaining usable capacity of a hybrid battery pack. One of the few parameters that speaks directly to a component's remaining service life rather than its present state. Electrical and Charging 0–100 %
• 5C Engine oil temperature Oil temperature, which under sustained load runs considerably hotter than coolant. This is why oil over-temperature can occur with an entirely normal-looking temperature gauge, and why this parameter is worth watching when towing or on track. Engine Management and Sensors -40 – 210 °C
• 5D Fuel injection timing When injection occurs relative to top dead centre. On a diesel this governs combustion noise, emissions and peak cylinder pressure, so a deviation is heard as much as measured. Fuel Delivery -210 – 302 °
• 5E Engine fuel rate Instantaneous fuel consumption. Comparing this against expected consumption at a known load is a quick way to confirm that a suspected rich condition is real rather than inferred from trim values. Fuel Delivery 0–3212.75 L/h
• 61 Driver's demanded engine torque Torque the driver is requesting, as a percentage of reference torque. Comparing demanded against actual torque is the cleanest way to quantify a limp mode — it shows exactly how much the module is withholding. Engine Management and Sensors -125 – 130 %
• 62 Actual engine torque Torque the engine is actually producing, as a percentage of reference. Well below driver demand with no stored code often means a boost or fuelling shortfall the module has not yet decided to call a fault. Engine Management and Sensors -125 – 130 %
• 63 Engine reference torque The reference figure the torque percentages are expressed against, which is what makes them convertible into actual newton metres. Engine Management and Sensors 0–65535 Nm

A snapshot of the same parameters as Mode 01, captured at the instant a fault was stored. Enormously useful for intermittent faults: it records engine speed, load, coolant temperature and fuel trim at the moment the problem occurred, which is often the only evidence available when the fault will not reproduce on demand.

Confirmed faults — those that have failed often enough to illuminate the warning lamp. This is what a basic code reader shows, and reading only this mode is why some faults get missed: a problem that has occurred once sits in Mode 07 instead.

Erases stored codes, freeze frame data and readiness monitor status. Worth understanding what it destroys: clearing codes also clears the freeze frame that would have explained them, and resets the monitors so the vehicle cannot pass an emissions test until it has completed a full drive cycle. Read the data before clearing it.

Oxygen sensor test results on older non-CAN vehicles. Superseded by Mode 06 on CAN-equipped vehicles, so on anything reasonably modern this mode returns nothing and the equivalent data lives in Mode 06.

Raw test results for each monitored component or system, with the measured value alongside the pass/fail limits. The most underused mode in the standard: it shows how close a system is to failing before it actually sets a code, which makes it the only way to catch a catalytic converter or oxygen sensor that is degrading but not yet faulty.

Faults detected during the current or previous drive cycle that have not yet failed often enough to illuminate the lamp. Checking here after a repair is how you confirm the fault has genuinely gone rather than merely not returned yet.

Allows a scan tool to command a component directly rather than just observe it — actuating a valve, running a pump, forcing a monitor to execute. Support is patchy and manufacturer-dependent, but where available it turns a passive diagnosis into an active test.

Identification data: vehicle identification number, calibration identifiers and verification numbers. The calibration ID matters diagnostically — it reveals whether a control module has been reprogrammed or retuned, which explains a class of faults that no sensor test will find.

• 02 Vehicle identification number The VIN as reported by the control module. Worth cross-checking against the VIN on the vehicle: a mismatch indicates a replacement module, which explains configuration faults that no sensor test will find. Engine Management and Sensors
• 04 Calibration identification The software calibration currently loaded. Reveals whether a module has been reprogrammed or aftermarket-tuned — which is directly relevant to overboost, overspeed and knock-related faults, and is otherwise almost impossible to establish. Engine Management and Sensors
• 06 Calibration verification numbers A checksum over the calibration, used to verify the software has not been altered. Some emissions inspections check this against a manufacturer database, so an unexpected value can fail a test on its own. Engine Management and Sensors

Confirmed faults that cannot be cleared with a scan tool. They erase only when the vehicle itself verifies the repair across a full drive cycle. Introduced specifically to stop codes being cleared immediately before an emissions test, so a vehicle presenting with permanent codes will fail regardless of what Mode 03 shows.