| 0x04 |
Engine Load (Calculated Load) |
% |
0–100% |
Represents the current engine load percentage. Normal can range from no load to full load (0-100%). At idle: approximately 15–25% is normal. City cruising: approximately 20–40%. If idle load is consistently above 30%, possible causes include intake carbon deposits or throttle body malfunction causing additional resistance. Sustained high load (>80%) can lead to engine overheating and carbon buildup – check for towing, hill climbing, or other heavy-load situations or engine faults. |
| 0x05 |
Engine Coolant Temperature |
°C |
70–105°C |
Indicates engine coolant temperature. Normal operating temperature is approximately 85–100°C (dashboard gauge should read around the middle). Temperature too high (>110°C): indicates possible overheating – causes include radiator fan failure, thermostat stuck closed, etc. Temperature too low (consistently below 70°C): thermostat may be stuck open or sensor is inaccurate; engine not reaching operating temperature will affect combustion efficiency and fuel consumption. |
| 0x06 |
Short Term Fuel Trim (Bank 1) |
% |
–5% to +5% (idle); –10% to +10% (cruising) |
ECU's instantaneous air-fuel ratio adjustment parameter. Normal STFT at idle should be within ±5%, and within ±10% during cruising, with continuous small fluctuations indicating the mixture is near stoichiometric. If STFT consistently exceeds ±10%, fuel adjustment is at its limit – possible causes include vacuum leak (high positive correction = adding fuel) or excess unburned fuel (high negative correction = reducing fuel). |
| 0x07 |
Long Term Fuel Trim (Bank 1) |
% |
–10% to +10% (typical); should not exceed ±20% |
ECU's cumulative fuel compensation value. Normal LTFT is around ±10%; values above ±15% indicate significant deviation. Consistently positive LTFT (>+15%): engine is running lean long-term (intake leak, insufficient fuel supply). Consistently negative LTFT (<–15%): mixture is running rich long-term (leaking injector, restricted intake). Values exceeding ±20% will typically trigger a trouble code. |
| 0x0A |
Fuel Pressure |
kPa |
300–400 kPa |
Fuel rail (fuel supply line) gauge pressure. Normal at idle is approximately 300–400 kPa (about 3–4 bar, or 30–50 psi). This range ensures proper atomization. Pressure too low (<250 kPa): insufficient fuel supply, possibly due to weak fuel pump or clogged fuel filter, causing lean mixture and reduced power. Pressure too high (>400 kPa): pressure regulator malfunction likely, causing rich mixture and increased fuel consumption. |
| 0x0B |
Intake Manifold Absolute Pressure (MAP) |
kPa |
20–100 kPa |
Reflects intake vacuum and engine load. At idle: manifold vacuum is high, absolute pressure is low – approximately 20–40 kPa is normal (e.g., typical sea-level idle ~27 kPa). At wide-open throttle (WOT) / high load: approaches atmospheric pressure, approximately 90–101 kPa. If idle pressure is abnormally high (close to atmospheric), indicates vacuum leak, camshaft timing error, or insufficient cylinder pressure. If still low at high-speed full load, may indicate clogged air filter or exhaust restriction. |
| 0x0C |
Engine RPM |
rpm |
700–6000 rpm (typical) |
Engine revolutions per minute. Normal idle: approximately 700–900 rpm (slightly higher during cold start or with A/C on); high-speed operation depends on vehicle – can reach 3000–5000+ rpm; redline is typically 6000–7000 rpm. Idle too high (>1000 rpm): possible IAC valve problem or vacuum leak. Idle too low or rough: possible ignition/fuel supply issues. Sustained over-rev operation damages the engine. |
| 0x0D |
Vehicle Speed |
km/h |
0–200 km/h |
Vehicle speed sensor reading. Normal range depends on driving conditions – city 0–80 km/h, highway can exceed 120 km/h. If vehicle is stationary but speed is non-zero or readings are erratic, possible speed sensor fault. Speed signal is used for transmission shifting and ABS/ESP systems – abnormalities can cause harsh shifts or affect stability control. Always obey speed limits – excessive speed is a safety hazard. |
| 0x0E |
Ignition Timing Advance (Relative to TDC) |
°BTDC |
–10° to +40° |
Engine ignition timing. Normal idle: ignition advance is around 5–15°BTDC (e.g., some vehicles ~+10° at idle). During light-load cruising, advance can reach 20–40° for improved efficiency. During acceleration/high load, ECU retards timing to prevent knock – advance decreases or even approaches 0°. If timing reads fixed/unchanging, possible knock sensor or ECU fault. If consistently very low or negative (late ignition), power will decrease and engine may overheat – check timing calibration. |
| 0x0F |
Intake Air Temperature (IAT) |
°C |
~Ambient temperature (–30 to +50°C) |
Measures temperature of air entering the engine. Under normal conditions, IAT should be close to ambient temperature: e.g., if outdoor temp is 20°C, IAT should be approximately 20–30°C, typically no more than 10°C above ambient (engine bay residual heat warms the intake). If IAT reads much higher than ambient (>30°C above), possible sensor fault or overheated intake manifold. If significantly lower than actual ambient, possible open sensor circuit. IAT affects air density and fuel injection calculations – inaccurate sensor causes air-fuel ratio deviation. |
| 0x10 |
Mass Air Flow (MAF) |
g/s |
Idle: 2–7 g/s; 2500 rpm: ~15–25 g/s |
Mass air flow sensor output indicating air mass flow into the engine. Values change with operating conditions: At idle: typically a few grams per second (proportional to engine displacement, typical 2–7 g/s). At medium RPM/load: tens of g/s. At WOT acceleration: can reach 100+ g/s (higher for larger engines). If idle MAF is significantly low (e.g., should be 5 g/s but reads 2 g/s), sensor may be dirty or vacuum leak causing inaccurate readings, leading to lean mixture. If idle MAF is too high, possible EGR leak or throttle body air leak causing over-reported airflow. |
| 0x11 |
Throttle Position |
% |
0–100% |
Accelerator pedal or throttle valve opening percentage. Normal range is 0% (throttle nearly closed at idle) to 100% (pedal floored, fully open). At idle: electronic throttle may maintain 5–15% to stabilize RPM. During acceleration: should increase smoothly toward 100%. If throttle opening cannot exceed ~80% with pedal floored, possible throttle or pedal position sensor fault limiting opening. If idle position is abnormally high, possible throttle body carbon deposits requiring greater opening to maintain idle, or IAC valve issue. |
| 0x14 |
Oxygen Sensor 1 Voltage (Front O2, B1S1) |
V |
0.1–0.9 V (oscillating) |
Narrowband oxygen sensor signal voltage upstream of catalytic converter. Under normal conditions, voltage rapidly oscillates between 0.1–0.9 V (low voltage = lean mixture, high voltage = rich mixture). This continuous oscillation indicates normal closed-loop air-fuel ratio control. If voltage stays fixed below 0.2 V for extended periods, indicates mixture too lean or aged/failed sensor. If fixed above 0.8 V, indicates mixture too rich or carbon-fouled sensor. O2 sensor signal abnormalities directly affect fuel trim – check sensor and related fuel/intake systems. |
| 0x2F |
Fuel Level Input |
% |
0–100% |
Fuel tank remaining fuel percentage. 100% = full tank, 0% = empty. Under normal conditions, fuel level gradually decreases with mileage. When fuel level drops below 15% (gauge approaching red), fuel pump may run dry and trigger fuel warning light – refuel promptly. Very low fuel can cause unstable fuel supply and pump overheating. If level reading doesn't match gauge or changes abnormally (e.g., stuck at one value), possible fuel level sensor fault or stuck float arm. |
| 0x42 |
System Voltage (OBD Voltage) |
V |
13.0–14.5 V (engine running); ~12.6 V (key off) |
ECU-monitored vehicle power voltage, generally close to battery voltage. With engine running: normal charging voltage is approximately 14±0.5 V (typical target 14.0–14.5 V). Key off (static): battery voltage around 12.6 V indicates normal full charge. If voltage is below 13 V at idle, indicates alternator charging insufficiency or belt slip – may cause battery drain. If consistently above 15 V, voltage regulator fault causing overcharge – may damage vehicle electronics. |
| 0x5C |
Engine Oil Temperature |
°C |
80–110°C |
Engine oil temperature parameter (available on some vehicles). During normal driving, oil temperature is typically 90–105°C (similar to or slightly higher than coolant temperature), ensuring proper lubrication. During aggressive driving or high load (racing, towing), oil temp can rise above 110°C, but should generally not exceed 120°C for extended periods – otherwise oil viscosity drops and oxidation accelerates. If oil temperature stays low (<60°C) for extended periods, engine may not be fully warmed up or thermostat (if equipped) may be faulty – this reduces lubrication efficiency and increases carbon deposits. Regular monitoring of oil temperature helps assess lubrication system health and prevent engine damage from overheating or insufficient warming. |