My 98 Jeep Grand Cherokee has a check engine light on...?

Question

When put on a diagnostic it read "Downstream O2 Sensor slow to react." The mechanic was very vague about what this was & cleared the message but it came back two days later. Can someone enlighten me with a little more detail & tell me where this sensor is located?
Thanks!

Answer 1

What that means is the downstream (post-catalytic converter) Oxygen Sensor is not switching normally. This can be viewed on a diagnostic scanner. Normally these sensors will switch rapidly from low to high readings which register on the scanner as a 3-digit number. In the course of a few seconds an O2 sensor can move up or down by several hundred units. A "slow to react" code means the sensor either isn't switching or is switching slowly or over a limited range. This is usually, but not always, due to a faulty O2 sensor.

Odd that this mechanic couldn't figure it out. O2 sensor tests are very straightforward.

You could just replace the sensor, have the light reset again and hope for the best but again, without a proper test this may not fix it. Probably but I won't guarantee it.

Answer 2

the o2 sensors are screwed straight into your exhaust. usually near the catalytic converter and one further down which is probably the one you're looking for.

the o2 sensor measures the oxygen content of the exhaust, information it relays back to the engine computer, and used to determine the correct air/fuel mixture.

its important to keep the o2 sensors working because if they're not delivering an accurate reading, your car's computer will run a richer fuel/air mixture to deliver needed performance.

but this also wastes gasoline, and you'll foul your catalytic converter and other emissions parts like the EGR valve (200$) with added emissions, and cause them to fail prematurely.

they're not too hard to take off though these sensors. once you know which one it is and what's going on put a box wrench on it and pull hard as you can. takes a lot of pulling to get them out cuz the heat just cooks them right in there. (make sure the tailpipe is cool) put the new one in nicely it doesn't have to be as tight and plug it in.

autozone will have new ones. i think they're like 50 bucks.

Answer 3

Those sensors are at the end of their life. Get some from Autozone for $40 apiece and change them. I have a 98 Grand Cherokee and they came out with an open end wrench with no problem.

Answer 4

a jeep grand cherokee has two o2 sensors one is near the top of the exhaust manifold the other is just before the catalytic converter.The second one is the downstream one.It is probably just going south but only partially.youwill have to have it replaced before a legal inspection could be performed.

Answer 5

A bad O2 sensor will affect your gas mileage.
I think there are 2 on a Honda Accord and there might be 2 on your Jeep. I got my diagnostic test at Auto Zone or one of those auto parts places for free and he explained where they are...my husband installed one and the other was too hard to get to so the dealer did it but it was under recall notice so it was free.

Answer 6

if the fault was for the downstream o2 sensor than that means it is the sensor after the catalytic converter. this sensor measures how efficiently the catalytic converter is working.

Answer 7

Modern cars are very good and reliable.

Engines are great, Sensors fail all the time.

There are thousands of people driving around with the check engine light on. Its the sensor.

I had an Acura with brake sensors on each wheel. 3 out of 4 sensors died. It cost me $200 per sensor to have them replaced.

Sensors ****

Answer 8

the reason the mechanic was so vague is that he could not properly diagnose the problem or tell you if it was a cat or a sensor problem. take it to another shop and have it diagnosed correctly

Answer 9

MY CHECK ENGINE LIGHT stayed on for years on my jeep. It baffled my mechanic where the sensor was, and it had no harm to my engine. I just accepted this a "quirk" of the jeep cherokee.