OBD code 171, 174
 

The wife's Expy,, developed rough idle, then check engine light..Pulled codes 171, 174..Can anyone help??

Thanks Ted

OBD code 171, 174
 

Code 171 and 174 are for bank 1 and 2 running too lean. The engine has compensated as rich as it can go, and it is still to lean. This does not necessarily mean your mixture is bad, but something (a sensor) is telling the ECM to correct lean. The oxygen sensors alert the ECM to how lean/rich the exhaust is, and then the ECM trips a code. Maybe you have a bad oxy. sensor, but since there are 4 of them (2 per bank), I don't think they could all go at once.

OBD code 171, 174
 

I had the same codes come up and it wasn't the sensor but it was the hose from the pvc valve to the intake system. It had small pin hose that was letting air into the system as was making my truck idle bad. Feel around to the back of the hose behind the air intake.

OBD code 171, 174
 

FTE is right, I forgot about that. I had the same engine issues, but not as bad. My PCV hose looked like it had been in the microwave for 20-30 minutes and barely allowed any air through it.

OBD code 171, 174
 

Thanks Guy's for the quick response..I'll check that out this AM..

OBD code 171, 174
 

Can not find any leaks in the intake system,,any other ideas ?
Thanks..

OBD code 171, 174
 

This appears to be a common problem!...I also have a 1998 Expedition EB 5.4L Triton (77k miles), and have a rough idle and "check engine" light warning. I just wanted to thank you all for this forum and great ideas that are shared. I am headed to Autozone this afternoon to see if I can get a code check to determine if I need to replace O2 sensors MAS, or a PVC valve (haven't inspected this yet).

The thought of taking my truck to a dealer and paying through the nose to fix this problem lead me here (that and the realization that I was looking at 4 O2 sensors to troubleshoot!). I appreciate the info that you all provide!

Question: Are the O2 sensors hard to get at/replace?

OBD code 171, 174
 

The PCV may look OK, but you have to trace the tubing back around to the back of the motor. It connects to the intake manifold with a small rubber elbow. This elbow, over time deteriorates from the heat inside the engine compartment. If you gently squeeze the elbow, you will feel the damage to it, it's probably cracked. It is almost impssoble to visually inspect due to its location. Check this out before going further, it may save you some $$$.

OBD code 171, 174
 

Thanks Rpt,,I'll check it tonight..

OBD code 171, 174
 

Replaced the PCV assembly and hoses,,That fixed the problem..Thanks Again for the help..

OBD code 171, 174
 

Thanks for the thread guy's. My 97 E350 check engine light came on 2 weeks ago. After replacing 2 O2's I looked here and found my PVC elbow was bad (it did look like it had been in a microwave)

Autozone's OBD said it was too lean, but no code. O'Riley's machine give me a code of 171,174. That's how I found this thread. If I looked here first, I might have saved $100.00 bucks.