DTCs P1128 and P1129

[Matt]

Well, my check engine light turned on today and those were the two codes I pulled.

P1128 - CLOSED LOOP FUELING NOT ACHIEVED - BANK 1
P1129 - CLOSED LOOP FUELING NOT ACHIEVED - BANK 2


When Monitored:
Engine running in closed loop mode.

Set Condition:
Enable conditions are met and the 02 sensor has not been in closed loop control at least once on each of the two consecutive trips, the MIL illuminates and the DTC is set. Two Trip Fault. Three good trips to turn off the MIL


Possible Causes

RESTRICTED FUEL SUPPLY LINE
FUEL PUMP INLET STRAINER PLUGGED
FUEL PUMP MODULE
O2 SIGNAL CIRCUIT
O2 RETURN CIRCUIT
O2 SENSOR HEATER OPERATION
O2 SENSOR
MAP SENSOR OPERATION
ECT SENSOR OPERATION
ENGINE MECHANICAL PROBLEM
FUEL FILTER/PRESSURE REGULATOR (HIGH)
PCM

This is a common occurrence on forums for guys who want to replace their 02 sensors just for the hell of it as part of preventative maintenance... and usually use generic or lower quality Bosch sensors which tend to be too slow transitioning for Chrysler vehicles.

Me? Well, I didn't change a thing and my Xk has 33k miles on it (thought it is an 07) so I doubt that both upstream sensors decided to fail at the same exact time.

If it comes back on i'll do some trouble shooting (check out fuel pressure, coolant temp and MAP readings) and go from there.

[Matt]

Well... these codes came back and are now coming on repeatedly.

Looks like i need to fix something

[Matt]

Well this is turning into a PITA.

ECT and MAP readings look good. Can't check fuel pressure yet, had to order special tool that goes between the fuel line and the fuel rail...
Doubt its an 02 issue, sensors are functioning properly and no other codes (normally you'll get an 02 sensor circuit fault).

I also doubt its the fuel pressure, but need to check it for peace of mind.

I'll probably replace the t-stat on Friday. Thinking that the t-stat could be getting stuck open on occasion which would make sense, and result in my intermittent condition. Past few times I drove the XK i had my scanner hooked up and was in closed loop within a minute...

Only other thing I could think of is they're running more than 10% ethanol at the gas station i've been going to, and the system is sensitive enough that it effects it. So i'll be keeping my eye out for TSB's since I doubt i'd be the only one that has this issue (note that there was already a software update for flex-fuel vehicles that had this issue)

[Matt]

Looks like i found my issue.... the tstat gasket tore/came loose and it looks like it was getting pinched, thereby keep the tstat from closing. Condition was intermittent because it wouldn't always stay like that. Hence, i wasn't having the issue right now, it seemed to have subsided again.

[NoMatter]

Sounds like a tough one to troubleshoot. Did the thermostat do the trick?

[Matt]

Nope... damn codes popped back on today.

I removed the Superchips tune. Going to run it stock for a while to make sure the codes come on with the stock programming. Next thing im going to do is try timing the 02 sensors to see how long they take to heat up; if they're close to the 40 second limit then i may try replacing them ($30/each isn't bad). If that's not it, I may be using my certified preowned warranty and letting my dealer take a look in case its the PCM.

[The_War_Wagon]

Nope... damn codes popped back on today.

I removed the Superchips tune. Going to run it stock for a while to make sure the codes come on with the stock programming. Next thing im going to do is try timing the 02 sensors to see how long they take to heat up; if they're close to the 40 second limit then i may try replacing them ($30/each isn't bad). If that's not it, I may be using my certified preowned warranty and letting my dealer take a look in case its the PCM.

So what finally happened?

[Matt]

02 sensors timed out OK.

Put the stock tune back in and just adjusted for tire size and haven't had the codes come back... yet...