2004 Jeep Grand Cherokee WJ 4.7L: P0172 and P0175 O2 Sensor Codes Causing Engine Stalling at Intersections
I've been experiencing a recurring engine stalling issue when approaching intersections, especially in coast mode. The problem is intermittent but noticeable—idle speed drops below 500 RPM, sometimes as low as 300 RPM, and the vehicle seems to be on the verge of stalling, though it often recovers. My scan tool shows pending OBD2 codes P0172 (System Too Rich Bank 2) and P0175 (System Too Rich Bank 1). These are oxygen sensor-related codes, but I can't see all four sensors clearly on the scan—only the left bank sensors appear to blink intermittently. The codes never appear as logged codes; they only show up as pending. They trigger when the engine is moved into drive and disappear during idle or under load. The issue does not occur when there's any mechanical load, such as climbing a slight incline—only in coast mode. Further diagnostics reveal PID03 = 0202, indicating an 'open loop' condition. I've already cleaned the throttle body (MOPAR model), replaced all emission hoses and joints, and removed the intake manifold to inspect the harness routing on the left bank. The problem started immediately after replacing the left rocker cover gasket. The vehicle has 160,000 miles on it. I suspect an aged or damaged wiring harness, especially in the left bank, given that the issue reappeared after disturbing the harness and convectors during maintenance. I've also noticed a crack in the crankcase vent hose—this was repaired, and the stalling began shortly after. I'm seeking advice on whether these codes point to faulty oxygen sensors or deeper issues like fuel trim imbalances, ECT (Engine Coolant Temperature) sensor problems, or an open loop due to wiring faults. I've done a basic fuel pressure test and leak-down check at idle, but results are inconclusive. I'm aware that K&N filters can interfere with emissions control—so I’ve avoided them. Any insights on diagnosing the root cause of these pending codes and stalling behavior would be greatly appreciated.
The OBD2 codes P0172 and P0175 do not indicate faulty sensors—they only show a system-wide issue. In this case, both banks are running too rich (system rich), meaning the oxygen sensors are signaling incorrect air-fuel ratios. An 'open loop' condition (PID03 = 0202) suggests the engine is not using closed-loop feedback control—this can be caused by a faulty ECT sensor, poor fuel trim response, or wiring issues in the O2 sensor harness. Check your ECT and fuel trims with a scan tool. Basic diagnostics to perform: - Fuel pressure test under idle conditions - Leak-down test at crankcase vent (KOEO) - Inspect all O2 sensor harnesses for chafing, especially on the left bank where you recently worked Avoid K&N filters as they can disrupt emissions control and trigger similar symptoms. Note: If these codes become logged instead of pending after further driving, it may indicate a more persistent issue—such as a failing sensor or intermittent wiring fault.