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I have a 2008 Range Rover HSE with 147,000 miles. I got a check engine light and the PID indicated catalytic converters in bank 2 were bad. I replaced the cats and then started getting P0171 and P0174 messages. I replaced the air filter and the MAF sensor and still getting the same messages.

The freeze frame info from the OBD scanner is as follows:

  Fuel System 1 CL
  Fuel System 2 CL
  Load %    47.8
  ETC°         189.0
  SHRTFT1   7.0
  LONGFT1   12.5
  SHRTFT2   -0.8
  LONGFT2   10.2
  MAP (inHg)    19.8
  RPM           1322
  VSS (MPH) 24
  Spark ADVC°   33
  IAT°          75
  MAF (lb/min)  2.930
  TP(%)        20.0
  RUNTM (SEC)   157
  EGR_PTC(%)    48.2
  EGR_ERR (%)   0.0
  EVAP_PCT (%)  36.1
  FLI (%)   45.9
  BARO (inHg)   29.2
  VPWR (V)  13.964
  Load_ABS (%)  42.7
  EQ_RAT    0.961
  TP_R (%)  8.2
  AAT (°F)  54
  TP_B (%)  36.1
  APP_D (%) 28.6
  APP_E (%) 28.2
  TAC_PCT (%)   30.2

Can anyone tell me what to look for or what to replace at this point?

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  • 1
    Have you checked for vacuum leaks in the intake manifold?
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jan 8, 2017 at 20:52
  • 1
    I would look first to the last area worked on before the symptom presented itself. The exhaust system; leaks anywhere near the oxygen sensor can cause mixture problems.
    – Fred Wilson
    Commented Jan 8, 2017 at 21:59
  • 1
    @Pᴀᴜʟsᴛᴇʀ2 I think manifold leaks are possible but less likely because the code set at road speed and load. In my experience intake leaks are more likely to cause fuel trim problems at low airflow, such as at idle.
    – Fred Wilson
    Commented Jan 8, 2017 at 22:05
  • @FredWilson - Good point on following up where the last work was done. The cats will be downstream of the area where a leak which would cause this would be, so if it was that, it would have to be some major tweakage to the exhaust system. Still, best place to start.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jan 8, 2017 at 23:14
  • What do the post-cat O2 sensors read?
    – Zaid
    Commented Jan 9, 2017 at 6:04

1 Answer 1

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In general, these codes indicate that the ECU receives information about fuel mixture being too lean, ie. too much oxygen, too little fuel. Therefore, it is trying to compensate by adding more fuel (see the long term fuel trim values which are pretty high). This is done according to A/F sensor readings.

Things to check:

  • MAF - hypothetically could be faulty, although new.
  • exhaust leak - oxygen getting into the exhaust system, confusing the A/F sensor. The mixture actually is not too lean but due to false sensor readings, ECU thinks it is. In my opinion not very probable option.
  • intake vacuum leak - unmetered air getting into the mixture (unmetered = after the MAF)
  • fuel pressure - fuel pump may not be providing enough fuel pressure
  • fuel injectors - might be clogged, not letting enough fuel into the intake
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4
  • The lambda sensors might be giving a false reading as well, although given the STFT and LTFT readings it's likely a case of unmetered air. Given the cat replacement preceding these codes, I agree that an exhaust leak is highly likely
    – Zaid
    Commented Jan 4, 2018 at 9:52
  • Well, I wrote that exhaust leak is not likely, as I think that it would be audible very well (given the leak would have to be situated around the exhaust manifold).
    – MaSlo
    Commented Jan 4, 2018 at 10:38
  • It could be around the cats as well
    – Zaid
    Commented Jan 4, 2018 at 10:39
  • Got it. I admit I don't know the exact exhaust system geometry for this exact car so you might be right.
    – MaSlo
    Commented Jan 4, 2018 at 10:46

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