Hi All!
I have a 1999 X cab 2 wheel drive Ranger 4.0 L auto. The CEL came on and I had Auto Zone pull the codes. I have a code P1151 which states "lack of HO2S21 switch - Sensor indicates lean" and a P0153 which states " Oxygen sensor 1 in Bank 2 was too slow during testing". My assumption is that I have a bad oxygen sensor in the manifold of Bank 2. The truck has 93,000 miles so that would not be surprising.

Is this a fair assumption? Is there any thing else I need to be concerned with? Auto Zone wants $50.00 for a new sensor so before I spend $50.00 and the time to replace it I thought I would ask the "experts" for advice. Any hints on replacing the sensor if that is what I need?

 

Well, normally when I see a P1151 code I would remind people that an O2 sensor indicating lean doesn't necessarily mean that there is anything wrong with the sensor ...instead, it can indicate that there is some kind of vacuum or exhaust leak, or fuel delivery issue etc. which is creating the lean condition.

However, since you are also getting the P0153 code, that tends to lend more credibility to the theory that the Bank 2 "upstream" sensor itself (or the circuit) is bad. But you still ought to look over the engine bay for any possible leaks in the vacuum lines, check also the PCV and EGR systems and hoses, and look for any exhaust leaks on Bank 2 (driver's side).

If you decide to replace the O2 sensor, think about spraying it down well beforehand with a good penetrating oil. You can buy or rent a special O2 sensor socket from most auto parts stores, but it's not absolutely critical. Don't forget to take off the cable from the negative battery terminal and to unplug the O2 sensor's harness connector before you start wrenching it. You'll want to put a little anti-sieze compound on the threads of the new sensor if they don't already come with it applied.

 

Thanks Rock. I knew I could count on you for a quick response. I will check for vacuum leaks prior to replacing the sensor. I did a quick scan and did not see any vacuum lines disconnected or visibly damaged but I will investigate further. I'll also check for an exhaust leak on bank 2. Is it a wise maintenance move to replace all three O2 sensors since I will likely be replacing the upstream one?

 

You might consider the other upstream sensor on Bank 1 while you are in there. Both upstream sensors are the most important, since they report back to the PCM what is going on with the air/fuel mixture for each repsective bank of cylinders. Upstream O2 sensors can actually degrade in performance, and fuel economy can suffer accordingly. On the other hand, the downstream sensor exists only to make sure the cat system is working properly. Downstream O2 sensors pretty much either fail or they work, there is no in-between that affects engine performance.

 

Thanks Rock. I think I will replace both upstream sensors while I'm at it.

 

Hi.

I see that you have helped someone else with the p0153 CEL code. I have the same problem. I appears as if the O2 sensor is easy to replace ONCE YOU CAN LOCATE IT! I am a complete newbie and am not sure where it is located? I have a 1996 Ford Ranger XLT. I will check under the hood. Is there a website/webpage that has a diagram of where they are located?

Thanks!

 

the o2 sensors are on the exhaust before the catalytic converter. check the exhaust manifold. im not sure if they put o2 sensors after the cat on 96 or not but check

 

P0153 = HO2S Sensor Circuit Slow Response (HO2S-21)

HO2S-21 is the #1 (upstream) oxygen sensor located on bank 2 (driver's side).

In other words, the 02 sensor you are looking for is located on (or just after) the exhaust manifold on the driver's side. IIRC, I had to get at it from underneath the truck on my '98.

 

Sorry for the idiotic question, but I know where the manifold intake is (I believe), but am not sure where the exhaust manifold is? I will get underneath the truck later today and see if I can find anything. What exactly does an oxygen sensor look like? Thanks!

 

The exhaust manifolds are bolted to the cylinder heads. They are heavy duty cast iron, you can't miss 'em. This link might help you visualize things:

Location of Heated Oxygen Sensors (Ford OBD-II)

 

the exhaust manifolds are usually covered in rust.

 

Thanks for the post. I will be searching for the sensor very shortly. I have been too busy to address the problem as of yet. This forum is amazing with the breadth of information and help people can give.

 

On the diagram, how hard is it to get to the Ho2S-21 sensor? I must have missed that. The only sensor I located was way down below the exhaust and was very visible. I went out to my truck and I can't see any upstream sensor (maybe it is hidden?) I notice that on your diagram there is an * stating that Many applications use only one (1) downstream HO2S, which may be why I only see that one? Thanks!

 

On the diagram, how hard is it to get to the Ho2S-21 sensor? I must have missed that. The only sensor I located was way down below the exhaust and was very visible. I went out to my truck and I can't see any upstream sensor (maybe it is hidden?) I notice that on your diagram there is an * stating that Many applications use only one (1) downstream HO2S, which may be why I only see that one? Thanks!

 

I had the P0153 CEL on my 1996 Ford Ranger XLT and today when driving around the CEL went off. Is that good or bad? I don't know. Why would the CEL just go off? Is the problem not persistent anymore? Is there a predetermined amount of time the CEL is on for the P0153? I have no idea? help?

thanks.