My Toyota Kluger (Highlander in the US) has been plagued by recurrent P0171, P0174 (lean fuel mixture) trouble codes ever since I bought it 2nd hand. Apart from the dashboard light, I've seen no other symptoms (other than the nagging impression it's been drinking too much, around 13L/100km). The car's been through several inspections, and no mechanic has come up with a solution other than simply clearing the code. I'd like to get to the bottom of this, to either save the car, and thus my pocket, from further trouble, or at least save myself some gas. I know there are various possible causes for P0171/P0174--vaccum leaks, dirty/defective MAF, outdated PCM, clogged fuel filter/injectors--and nothing replaces a down and dirty inspection, but some of these--e.g. vaccum leaks--may be quite small, and hard to detect in the usual alotted time for an in loco inspection. With the growing use of bluetooth OBD2 units amongst drivers, I wonder whether there already are online mechanics helping drivers narrow down causes based on log data over longer time periods. Are there? I searched far and wide, yet to no avail.
UPDATE: @GdD commented that what [I'm] describing is not a mechanic problem but a data analytics platform; mapping causes and codes to features of the OBD data feed. Yeah, no, I'm not looking for an automated solution; that's a whole other kettle of fish. I am indeed looking for human assistance in narrowing down causes, even if at a distance (and that could be from anywhere in the world!), using not only OBD logs and monitors but also my own experience and observation driving the car. Incidentally, I've just come across a writeup of the sort of assistance I'm after (I'll try these, but if they don't work, I'd like to pay someone for further instructions on tests I could do nail the cause, before taking the car to a hands-on mechanic, so that I know exactly what service to order):
MIL illumination with trouble codes P0171 and P0174. The engine runs fine. The fuel filter was changed.
- Monitor the Long-Term Fuel Trim (LFT) readings at idle and at cruise speed to determine when it is lean.
- If the readings are highest at idle, look for a vacuum leak.
- If the LFT numbers are higher at cruise speed, monitor the fuel pressure and check for a dirty Mass Air Flow (MAF) sensor. Try cleaning the MAF sensor and recheck operation.
- If the MAF sensor is clean, monitor the fuel pressure. It should be roughly 30-45 psi and increase under load. Check voltage between the white and white/red wires at the fuel pump. At idle it should read 6-8 volts.
- If the fuel trim readings look good under all driving conditions, reprogram the PCM per TSB 07-21-7 if it has not previously been done.
- Engine Vacuum Leak
- Fuel Pump
- Mass Air Flow (MAF) Sensor
- Powertrain Control Module (PCM) Programming