P0106: MAP sensor range/performance and the vacuum leaks behind it
P0106 compares manifold pressure against what the ECU expects from throttle position and RPM. Most of the time the sensor is honest and the intake is leaking.
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P0107 and P0108: MAP circuit low and high — hose, connector or sensor
These are electrical codes, and the electrical part is usually intact. What fails is the vacuum hose feeding the sensor, and that costs almost nothing to check.
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P0111 and P0112: intake air temperature sensor faults
The IAT sensor corrects fuelling and ignition timing for air density. A wrong reading does not stop the car, it just makes everything slightly worse, all the time.
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P0116 to P0119: coolant temperature sensor performance and intermittent faults
The coolant sensor drives fuelling, fans, the gauge and the heater. A drifting one causes four unrelated-looking complaints, and the thermostat gets blamed for all of them.
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P0121 to P0123: throttle position sensor circuit faults
On a drive-by-wire engine the throttle sensor is a safety-critical input, which is why these codes send the car into limp mode rather than tolerating an error.
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P0130 to P0134: upstream oxygen sensor circuit and no activity
P0134 is the one that matters here: no activity detected. It means the sensor never woke up, and that changes what you check first.
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P0131 and P0132: oxygen sensor voltage stuck low or high
A narrowband oxygen sensor should swing constantly. These two codes fire when it stops swinging and parks at one end. The cause is often the mixture, not the sensor.
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P0133: slow oxygen sensor response — the code that precedes P0420
P0133 measures how fast the upstream sensor reacts, not what it reads. Catching it early is what stops it turning into a catalyst code and a four-figure bill.
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P0138 and P0140: downstream oxygen sensor high voltage and no activity
The rear sensor does not control fuelling — it grades the catalyst. That changes what these codes mean and why replacing the sensor sometimes fixes nothing.
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P0148: fuel delivery error on a diesel — commanded versus achieved
The ECU asked for a fuel quantity and did not get it. That is a whole-system verdict, not a component fault, which is why the code names nothing specific.
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P0170 and P0173: fuel trim malfunction, and why it is not the same as lean
P0171 says the mixture is lean. P0170 says the correction system itself has run out of authority. The difference decides where you look.
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P0176 to P0178: flex fuel composition sensor faults
On a flex fuel vehicle the ECU measures ethanol content in real time. When that sensor fails, the engine falls back to a safe assumption and you feel it.
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