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The Depressed Jeep

My 2007 Jeep Grand Cherokee has been ill ever since I bought it three years ago.   The Check Engine was on and it throws a code of P013C, “O2 SENSOR 2/2 SLOW RESPONSE – RICH TO LEAN”.   This is an unfixable plague for Jeep owners, and has become known as “the AIDS of Jeeps”.   So I bought a cheap OBD2 bluetooth dongle and an excellent Android phone app called Torque.   Checking my car’s oxygen sensors on engine bank 1 (driver’s side), I had what I should have:

Torque_WK_bank1

Notice that oxygen sensor 1 (upstream from the catalytic converter) goes rich/lean/rich/lean (more O2/less O2/more O2/less O2) just as it should, with the engine computer constantly adjusting the mixture to get the optimal burn of 1 part oxygen to 14.7 parts other exhaust gases.   And sensor 2 (downstream from the cat) is nice and steady, so the cat is doing its job. Well, here’s bank 2 (passenger’s side):

Torque_WK_bank2

Eh heh, pretty screwy.   Error code P013C says ‘O2 sensor 2/2 slow response’, and this kind of signal would account for it.   The car had a ‘spell’ 20 minutes after I bought it, where I got the distinct impression it had blown out a catalytic converter.   Sensors 1 and 2 looking about identical would confirm this, so I took the car to Bucky’s Muffler and had the bank 2 cat replaced.   Now the downstream sensor 2 looked alot more legitimate, but sensor 1 was still screwy.   Why?

It must be something upstream since it’s sensor 1.   I thought about it a while and decided that it can only be the plugs, or the coils on each plug.   So I bought a set of plugs, gapped them to .044″, and replaced them.   They sure needed it as the old ones had worn to .064″.   But while replacing plugs 4 & 5 I noticed there was brown grass down in the plug hole.   And the coils and plugs were corroded.   A mouse nest between the intake manifold and block, and the plug holes were their toilet!   So I replaced the coils for 4 & 5 (bank 2), started the engine, and sure enough the O2 signals are now fine.   So I cleared the P013C code and took the car on the highway grinning like I was sh*ttin’ in tall cotton.

No.   Another Check Engine.   And it was P013C.   How could this Be?   I’d replaced everything on bank 2, including both O2 sensors.   So I took the car back to Bucky’s Muffler and complained that they must have put in a regular catalytic converter, rather than a California cat as specified on the hood sticker.   They put their best guys on it and after a while they called me in.   They showed me their code scanner which said that P013C is BANK 1.   I couldn’t believe it because of the top 20 internet sites I’d checked, 7 specifically said it is bank 2, as did a forum poster named JeepCares and another poster who was definitely with Jeep corporate. (the rest didn’t specify)   But the fact was that bank 1 sensor 2 (downstream) signal had never moved, and it should.   Further, I finally realized it was too rich at .9v.   So I went home and replaced the 1×2 O2 sensor.   Took it for a test drive and sure enough, no more P013C.

So I had been having two problems all this time:   The corroded coils which eventually caused the cat to blow out;   and the bad sensor 1×2.   And no wonder that P013C has been such a plague…   all the information on The Internets is wrong, including that from two who work for Jeep!   Sure, I’d mistaken bank 1’s .9v signal as being good, but in fact it never changed;   it should go toward .1 on decel, and in stable-state should stay around .6v-.7v.   Unfortunately no one knows this but me…   A steady .9v, if anyone (besides a few silent Jeep techs) would have known this, was just wrong.

For the first time in three years the car now runs great.   The throttle responds sooner, indicating that both banks are pulling like they should, and the fuel economy is better too.   For future reference, here’s approximately what the two banks are supposed to look like, with cruise set to 65mph on flat open highway:

Torque_WK_bank1-fixed Torque_WK_bank2-fixed

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