04 Grand Caravan Poor Mileage / O2 sensor heater

[DJSteve]

I bought a 2005 Grand Caravan about a month and a half ago from a private party. It has the 3.3L engine and just over 80k on the clock.

Upon driving it on a few trips, it seemed sluggish and was getting poor mileage--around 16 mpg with all highway driving. I started by replacing the spark plugs and upstream oxygen sensor. The next trip--about 80 miles one way--everything seemed fine. When I got ready to come home, though, the check engine light came on. It seemed to be running OK so I drove it home and scanned codes the next morning--got a misfire on cylinder one and oxygen sensor heater circuit.

I *think* the misfire was a result of my cracking the porcelin of the #1 spark plug when I installed them. At least a piece fell out and that code hasn't recurred. When I swapped that out for a new plug I also replaced the wires.

I asked about the 02 sensor at the parts store (O'Reillys - Bosch sensor) and they said to just bring it in and swap it for a new one. So I did that, and got basically the same result. OK for the initial trip and then CEL with the oxygen sensor heater code upon the next startup.

Throughout this, I'm still getting ~16mpg with all highway driving. I've been running regular (87) even though 89 octane ethanol blend is cheaper here.

Any ideas what's causing the 02 sensor failures? I'm about ready to put the original one back in and ask Oreillys for my money back.

Or any ideas on what could be causing the poor fuel mileage? Any chance the two are related? Tires are properly inflated and I haven't noticed any signs of the brakes dragging. Spark plugs were replaced with OEM (Champion) and plug wires were the "premium" set that Oreillys carried (I believe Borg-Warner brand).

[jpb53]

Do yourself a favor. Return the Bosch sensor get your money back and buy a sensor at the dealer. You and your van will be happier. Try this site http://www.moparpartsamerica.com/spl...?siteid=214583 56029052aa is what I come up with for upstream O2 without flex fuel. Price is $53.42. 56029085aa is for flexfuel and is $41.53 from this company

[jmeuchel]

I just registered on this site to do a search on the same exact problem. Code P0135 -Bad Heated O2 circuit- Replaced worked fine for a couple 50mi trips now CEL has come on Code P0135. Any other ideas. Thanks in advance.

[DJSteve]

My issue is still unresolved. I put the original O2 sensor back on about a week ago and still have CEL, but have not had time to clear codes so I'm not sure if I'm seeing the same symptom or if it's just stored.

jmeuchel, are you seeing poor gas mileage as well or just the O2 sensor failure? Being in ND (rural?) has your van been driven much on gravel roads? The previous owner of my van lived several miles off the highway. Even after a couple trips to the car wash there seems to be gravel dust EVERYWHERE and I've wondered if that could somehow be a factor (i.e. plugged vents on some of the emission gear).

I also experienced another issue Saturday, which I'm not sure if is related or not. It was pretty hot/humid here and when driving to the wedding I was DJing for (only a few miles away) I started getting lurching around 3500 rpm in 1st gear every time I'd take off from a stop. Upon letting off the throttle it would downshift and everything would be fine. I was able to repeat this 3-4 times consistently, however when driving home at the end of the night everything was normal.

[jpb53]

It is a 2 trip fault. 5 volts is sent to the heater from the PCM. Heater resistance is 3 to 4 ohms.

[jpb53]

Fuel mileage is not going to get any better until you get the CEL off. The computer is programmed to keep the engine running which it is. Safeguard the engine while it is running with a faulty sensor that it can't trust like yours. A richer fuel mapping program is used to protect the engine from damage. Richer is better than leaner in this case. Richer for too long can eventually destroy a catalytic converter though.

[jmeuchel]

In my case I have reset the CEL and now it has coded again -P0135- Heater circuit failure. Same as first two times.

[DJSteve]

I think my O2 sensor issue has been resolved after putting the OEM one back and clearing codes. However, I'm now getting a P0016 (cam / crank position sensor discrepency). After doing some reading online I became suspicious my flexplate was cracked so I hooked up an oscilloscope and confirmed that the crank signal is behind what it should have been.

From what I've seen, the cracked flexplate seems consistent with power/mileage loss, so I'm hoping that's the only thing wrong. Now I just need to decide if I'm going to take it to a shop or try to do the work myself...

[hundahunta]

very common problem, if your scanner can read cam and crank difference it'll verify a cracked flexplate

[DJSteve]

I decided to take the plunge on changing out the flexplate myself. I wouldn't specifically reccommend it. There are a lot of bolts that are a total PITA to get to, and I've come to the conclusion that Chrysler's wiring connectors (and especially their secondary lock mechanisms) blow goats.

For anyone interested, I'm including pictures below. The crack is the darker fine line just outside the crankshaft bolt pattern. Holding it up to the sky, I could literally see daylight through the crack in places.

You'll notice it cracked right along the circular ridge. That isn't surprising (ridge in metal=focusing of stress), however I'm completely baffled why there's a ridge there in the first place. As far as I can tell it serves no real purpose--the area the crankshaft attaches to is on the same plane as the rest of the flexplate.

I saw reference elsewhere of Chrysler putting out a revised part--does anyone know any specifics on that? The new flexplate looks to be identical at least in terms of the stamping.

The second picture is after a light tap with a hammer--a bit disturbing to think this was the only thing coupling the engine to the tires.