Code P0030: lambda sensor heater control (bank 1 sensor 1)

All three affect the front lambda sensor on bank 1, the one before the catalytic converter, but different parts of it. The P0130 points to the circuit of the sensor itself, the one that transmits its oxygen signal. The P0030 and P0135 point to the heater that brings the sensor up to its operating temperature: the P0030 is defined as a fault in the control circuit of that heater (open circuit, short circuit or out-of-range values) and the P0135 as a malfunction of its circuit. The 2011 Saab 9-5 workshop manual shows how they are divided up: P0030 for the control circuit, P0053 for the heater resistance and P0135 for its performance. In all cases, the heater diagnosis is similar: fuse, wiring and resistance.^{[2][4][17][18]}

It is the same type of fault, but on a different sensor. The P0030 refers to the heater of the front sensor on bank 1 (sensor 1, before the catalytic converter); the P0141 refers to the heater of the rear sensor on the same bank (sensor 2, after the catalytic converter), and its 'control circuit' equivalent is the P0036.^[2][4][16]

Yes, for a while: Carista classifies it as low severity and Autodoc Club says it poses no risk to the car or the occupants, although it asks for it to be repaired with moderate urgency. While it lasts, the sensor takes longer to become useful after each start and the mixture is regulated less well, so it is worth fixing soon.^[1][6]

Not straight away. First the fuse (and relay), connector and wiring are checked, and the heater resistance and the supply and earth of its circuit are measured. The sensor is only replaced if those checks are fine and the heater is out of specification; if the fault were in the control unit, replacing the sensor would not fix it.^{[1][6][14][15]}

The sensor only measures oxygen properly when it is at about 300 °C. The heater brings it to that temperature in a short time after starting and helps keep it there at idle; without it, the sensor would take several minutes to become useful, and during that time the control unit cannot correct the mixture using its signal.^[5][16]

All three are the same control circuit for the front bank 1 sensor heater: the P0030 is the general fault and the P0031 and P0032 narrow it down to low and high level. For the P0031, TaT speaks of a low voltage or a high current in the circuit, which is 'pulled' to earth; Autodoc Club, of a heater resistance lower than optimal because of a short circuit in the heater; and Carista, of a control wire short-circuited to earth or a short-circuited heater. For the P0032 the sources do not agree on the electrical origin: TaT attributes it to an open heater or to excessive resistance in the earth or the control wire; Carista, to a control wire short-circuited to positive or to a faulty driver in the control unit, which would leave the heater permanently switched on and could overheat the sensor; and Autodoc Club speaks of excessive current draw. That is why it is worth measuring the circuit with a multimeter rather than relying on the code alone.^{[8][9][10][11][12][13]}

If the code has switched on the engine warning light, no: with that light on, the inspection records a serious defect, and on Euro 5 and Euro 6 cars the ITV (Spain's roadworthiness inspection, similar to the MOT) also reads the OBD diagnostic system. Repair the fault before you go; clearing the code just before the inspection does not help either, because it counts as a serious defect.^[19]