Scanner code 172 HEGO sensor voltage indicates lean

GM94

MEMBER
1917 FORD WINDSTAR

Hi all. I'm back with another problem ><. Grand Marquis 94 135k miles. Recently I fixed my low egr flow problem. I removed the air intake, cleaned the the ports including the ones for the egr. The car was running good with no engine light.

Next day I decided to change the egr valve as a precaution (dummy me) and installed a new one. I also changed my spark plugs. When I started the car it felt different right away. I can fell the engine hesitate a bit, which it wasn't happening before.

I decided to put everything back to normal, so I put back my old spark plugs and egr valve. That didn't solve the problem unfortunally. I didn't replace the spark plug cables(not sure if that will solve the problem). I did bought the same spark plugs, brand new but still didn't solve it. I also noticed a humming noise that is coming from the transmission area when you turn the key switch on without starting the engine(not sure if is normal), there is a wire harness that connects on the driver side on the transmission. When I unplug it the humming sound stops. Anyway back to my original problem.

Now i'm getting scanner code 172 : Heated Exhaust Gas Oxygen (HEGO) sensor- voltage signal indicates "lean" (bank #1). I just noticed that there is another HEGO sensor (i just only seen one) and it hasn't been replaced. Could it be bad? I did replace the other one. Any ideas or suggestions? Please help!

I just lerned that if the car is running fine. DON't mess with it, LOL

1 Reply

PEPPERMRJ

MECHANIC
1,158 POSTS

Basically this means that an oxygen sensor in bank 1 detected a rich condition (too little oxygen in the exhaust).

A code P0172 may mean that one or more of the following has happened:

The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters (K&N, etc.) Can cause the MAF to become dirty if the filter is over-oiled
There could be a vacuum leak.
There could be a fuel pressure or delivery problem

Possible solutions include:
Inspect all vacuum and PCV hoses, replace if necessary
Cleanthe MAF sensor. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
Inspect fuel lines for cracks, leaks, or pinches
Check the fuel pressure at the fuel rail
Check the fuel injectors, they may be dirty. Use fuel injector cleaner or get them professionally cleaned/replaced.
Check for an exhaust leak before the first oxygen sensor (this is unlikely to cause the problem, but it is possible)

Good hunting. :)