Look up an OBD2 fault code.

The engine computer has detected a general fault in the mass air flow (MAF) sensor circuit, which measures how much air is entering the engine. Without a trustworthy airflow reading the computer cannot meter fuel accurately.

The MAF sensor is responding, but its airflow reading is outside the expected range for current engine conditions — the value is implausible rather than simply missing.

The signal from the MAF sensor is lower than the computer expects — it is reading too little airflow, often because the circuit is shorted, disconnected, or the sensor is dirty.

The MAF signal is higher than expected — the sensor is reporting more airflow than is plausible for the current engine state.

The manifold absolute pressure (MAP) sensor reading is out of the expected range. MAP is used to estimate engine load, so a bad value upsets fuel and timing.

The intake air temperature (IAT) sensor signal is too high, which corresponds to an implausibly cold (or open-circuit) reading. The computer uses intake-air temperature to fine-tune the fuel mixture.

The engine took too long to reach normal operating temperature, or never reached it, in the time the computer expected. The usual cause is a thermostat stuck open so the engine runs too cool.

On bank 1 the computer has had to add fuel beyond its normal range because the mixture is running lean — there is too much air, or too little fuel, relative to the ideal ratio.

On bank 1 the mixture is running rich — too much fuel relative to air — and the computer has had to pull fuel out beyond its normal range to compensate.

The same lean condition as P0171, but on bank 2 — the cylinder bank that does not contain cylinder 1. Seen on V6/V8 engines.

The rich-mixture condition of P0172, but on bank 2. The computer has had to remove fuel beyond its normal range on that bank.

The manifold absolute pressure (MAP) sensor signal is lower than expected, often an open or shorted circuit or a sensor reading no vacuum. The computer uses MAP to estimate engine load.

The throttle position sensor (TPS) signal is lower than expected, telling the computer the throttle is less open than it really is. The TPS reports how far the throttle is open.

The throttle position sensor signal is higher than expected, telling the computer the throttle is more open than it really is.

The computer's fuel-trim corrections on bank 1 have reached their limit — it can no longer keep the air-fuel mixture in range, whether too rich or too lean.

The computer has detected misfires that are random or spread across more than one cylinder, rather than isolated to a single cylinder. A misfire is a combustion event that failed to happen properly.

A misfire has been detected specifically on cylinder 1. The last digit of a P030X code is the cylinder number, so this points you straight at one cylinder.

A misfire has been detected on cylinder 2 specifically.

A misfire has been detected on cylinder 3 specifically.

A misfire has been detected on cylinder 4 specifically.

A misfire has been detected on cylinder 5 specifically.

A misfire has been detected on cylinder 6 specifically.

The computer detected misfires during the first ~1000 engine revolutions after start-up. It usually appears alongside specific misfire or fuel codes that point to the underlying cause.

An electrical fault (open or short) in the fuel-injector circuit for cylinder 1. The injector may not be firing, which usually causes a misfire on that cylinder.

The catalytic converter on bank 1 is not cleaning the exhaust as efficiently as the computer expects. It judges this by comparing the upstream and downstream oxygen-sensor signals. The code names the symptom, not always the broken part.

The same low-catalyst-efficiency condition as P0420, but on bank 2 of a V6/V8 engine.

The exhaust gas recirculation (EGR) system is flowing less exhaust back into the intake than expected. EGR lowers combustion temperature to cut emissions; too little flow trips this code.

A general fault in the evaporative-emissions (EVAP) system, which captures fuel-tank vapors and routes them to the engine instead of venting them to the air.

The EVAP system has detected a small leak — a vapor leak too small to be a gross failure but large enough to fail the self-test.

The EVAP system has detected a large (gross) leak — a major escape path for fuel vapor, or no flow where flow is expected.

The EVAP self-test attributes a leak specifically to the fuel-fill cap being loose or off — many vehicles set this exact code when the gas cap is not sealed.

The EVAP system is not purging fuel vapor at the expected rate — either too much or too little flow through the purge valve when the engine draws stored vapor into the intake.

A circuit fault in the EVAP vent valve, which controls how the charcoal canister breathes during the system's leak self-test.

The EGR system is flowing more exhaust into the intake than expected — the opposite of P0401. Excess EGR upsets combustion, especially at idle.

The upstream oxygen sensor on bank 1 is reporting a persistently low voltage, which corresponds to a lean exhaust signal (or a circuit fault). Sensor 1 is the upstream sensor used for fuel control.

The downstream oxygen sensor on bank 1 (sensor 2, after the catalytic converter) is reporting a persistently low voltage. The downstream sensor is used mainly to monitor catalyst efficiency.

The heating element inside the upstream oxygen sensor on bank 1 has a circuit fault. The heater brings the sensor to operating temperature quickly so fuel control can begin sooner.

The upstream oxygen sensor on bank 1 is switching between rich and lean too slowly. A sluggish sensor degrades fuel control and emissions even though it still responds.

The heater element in the downstream oxygen sensor on bank 1 (after the converter) has a circuit fault, so it does not reach operating temperature on schedule.

The downstream oxygen sensor on bank 1 is reporting a persistently high voltage, corresponding to a rich exhaust signal or a circuit fault at sensor 2 (after the converter).

The engine coolant temperature (ECT) sensor signal is too low, corresponding to an implausibly hot reading or a short in the circuit. The computer uses coolant temperature for fueling and fan control.

The ECT sensor signal is too high, corresponding to an implausibly cold reading or an open circuit. The computer may default to a fixed temperature value.

The intake air temperature (IAT) sensor signal is too low, corresponding to an implausibly hot reading or a short in the circuit.

The engine coolant temperature (ECT) sensor is reading a value that is in range electrically but implausible for the conditions — for example, not changing the way a warming engine should.

The engine has not reached the temperature needed to enter closed-loop fuel control (where it trusts the oxygen sensors) in the expected time — typically because it is running too cool.

The intake camshaft timing on bank 1 is more advanced than commanded, or the variable-valve-timing (VVT) system is not responding correctly. Modern engines vary cam timing to optimize power and economy.

The exhaust camshaft timing on bank 1 is over-advanced or not tracking the commanded position. Same VVT family as P0011 but on the "B" (exhaust) camshaft.

A fault in the crankshaft position sensor circuit. This sensor tells the computer engine speed and crank position, which it needs to control spark and fuel timing.

A fault in the camshaft position sensor circuit. This sensor identifies which cylinder is on its compression stroke so the computer can time spark and injection correctly.

A circuit fault in knock sensor 1. The knock sensor listens for detonation (pinging) so the computer can retard timing to protect the engine. With it faulted, timing is managed conservatively.

The engine is idling slower than the computer's target idle speed. On modern throttle-by-wire engines this usually reflects a restriction or load the computer cannot overcome at idle.

The engine is idling faster than the computer's target idle speed — it cannot pull idle down to where it wants it, usually because extra air is getting in.

A fault in the vehicle speed sensor signal. The computer relies on vehicle speed for transmission shift logic, cruise control, and speedometer operation.

This is a general request from the transmission control module telling the engine computer that the transmission has stored its own fault. P0700 itself has no specific meaning — it points you to read the transmission's accompanying code(s).