Jeep P1129 Code: Closed Loop Fueling Not Achieved (Bank 2)
The PCM couldn't switch bank 2 of your Jeep's V6 or V8 into oxygen-sensor-controlled fueling in time.
At a glance
Severity: Low
- Meaning
- Closed Loop Fueling Not Achieved (Bank 2)
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $0–$900
- DIY difficulty
- Moderate
After a cold start the PCM runs the engine on preset fuel tables (open loop) and switches to closed loop once the upstream oxygen sensors are warm and switching rich-lean. P1129 sets when bank 2 doesn't make that switch within the expected time after the entry conditions are met, meaning the PCM never got a usable signal from sensor 2/1 or the mixture on that bank stayed too far off. It applies to Jeep V6 and V8 engines such as the 3.6 Pentastar, 3.7, 4.7 and 5.7 HEMI; bank 2 is the side without cylinder 1, which is the passenger side on the HEMI, 3.7 and 4.7 but the driver side on the Pentastar. Its twin, P1128, points to bank 1.
Can I keep driving? The engine is safe to drive, but bank 2 runs on default fueling, so mileage drops and the catalytic converter can suffer if it lasts for weeks. Plan the repair soon.
How to read P1129
- P Powertrain
- 1 Manufacturer-specific
- 1 Fuel & air metering
- 29 Specific fault
Symptoms
- Check engine light on
- Lower fuel economy
- Slightly rough or rich-smelling idle, especially when cold
- Often no noticeable drivability change
- Catalyst or O2 readiness monitors not completing
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Slow or failed bank 2 upstream O2 sensor (2/1)
- O2 sensor heater circuit fault: blown fuse, heater open, damaged wiring
- Exhaust leak ahead of the sensor, e.g. broken exhaust manifold bolts
- Sensor connectors swapped between banks or wrong sensor installed
- Sensor wiring melted or chafed on the exhaust
- Bank 2 mixture fault: intake leak or weak injector
- PCM software needing an update
Diagnosis step by step
Read all codes and fuel status
Look for companion codes such as P0151, P0153 or heater code P0050, which make the diagnosis much faster. In live data, check the fuel system status for each bank after warm-up: bank 1 in closed loop and bank 2 stuck in open loop confirms the problem.
Tools: OBD-II scanner
Compare sensor 1/1 and 2/1 signals
Hold the engine around 2,500 rpm when fully warm and graph both upstream sensors. A healthy sensor swings between roughly 0.1 and 0.9 V several times a second; a flat or sluggish 2/1 compared with 1/1 identifies the sensor or its circuit.
Tools: OBD-II scanner
Check the heater circuit
Unplug sensor 2/1 and measure heater resistance across the heater pins; it should be a few ohms, not open. Confirm 12 V on the heater feed with the key on and check the fuse and ground on the harness side.
Tools: Multimeter
Look and listen for exhaust leaks
On a cold start, listen for ticking at the bank 2 manifold that fades as it warms, and look for soot streaks at the manifold flange. On HEMI engines check for broken manifold studs; outside air pulled in past a leak skews the sensor reading.
Tools: Flashlight
Verify connectors after any O2 sensor work
If sensors were replaced recently, trace each sensor's pigtail to its connector. Bank 1 and bank 2 plugs can be crossed on these engines, which sets P1128 or P1129 right after the repair.
Tools: Flashlight
Rule out a bank 2 mixture problem
Smoke-test the intake for leaks near bank 2 runners and compare long-term fuel trims between banks. A bank 2 trim much higher than bank 1 points to air or fuel delivery, not the sensor.
Tools: Smoke machine, OBD-II scanner
Where the parts are
- 1Upstream O2 sensor
- 2Catalytic converter
- 3Downstream O2 sensor
- 4Diesel particulate filter
- 5Turbocharger
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Correct swapped connectors or repair sensor wiring | Yes | $0–$200 |
| Replace upstream O2 sensor bank 2 (2/1) | Yes | $150–$350 |
| Repair broken exhaust manifold bolts or gasket | No | $300–$900 |
| Repair intake leak or replace injector | No | $150–$450 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Ram
Ram trucks with the 5.7 HEMI use the same P1128/P1129 logic, and broken exhaust manifold bolts on the passenger side are a common reason bank 2 won't reach closed loop.
Jeep
On Grand Cherokee and Commander with the 5.7 HEMI, cracked or snapped exhaust manifold bolts are a well-known source of ticking on cold starts and of exhaust leaks that upset the bank's upstream O2 sensor.
Emissions / smog test impact
Will fail
P1129 turns on the check engine light and can keep O2 and catalyst monitors from completing, so the vehicle fails an OBD emissions test until it's fixed and the monitors have run.
Frequently asked questions
Which side is bank 2 on my Jeep?
Bank 2 is the side that doesn't contain cylinder 1. On the 5.7 HEMI, 3.7 and 4.7 that's the passenger side; on the 3.6 Pentastar it's the driver side. Confirm with your engine's cylinder numbering before buying a sensor.
I just replaced my O2 sensors and now have P1129. What went wrong?
Most often the bank 1 and bank 2 connectors were swapped or a sensor was installed on the wrong side. Trace each pigtail to its plug; fixing the routing usually clears the problem.
Is P1129 the same as P1128?
Same logic, other bank. P1128 means bank 1 didn't reach closed loop; P1129 means bank 2 didn't. If both set together, look for something common such as a fuse feeding both heaters.
Can I just replace the O2 sensor?
It's the most likely fix, but check for heater codes, exhaust leaks and swapped connectors first. A new sensor won't help if a leak or a blown fuse is the real cause.
Sources
- Manufacturer public service information (cross-checked)
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