P1153 indicates that the engine control module (ECM) has detected a lean mixture on bank 2 and, after attempting to correct it by adjusting fuel trim, the condition persists. The code is set when the oxygen sensor on bank 2 reports a low voltage for a sustained period, signaling that the air‑fuel ratio is leaner than the commanded target. This can be caused by a faulty sensor, a fuel‑delivery problem, an air leak, or, much less commonly, an ECM issue.
The upstream oxygen sensor on bank 2 may produce incorrect voltage readings, causing the ECM to believe the mixture is lean even when it is not.
Unmetered air entering the intake manifold (e.g., from a cracked hose or gasket) creates a lean condition that the fuel system cannot compensate for.
Insufficient fuel delivery due to a weak pump, clogged filter, or faulty pressure regulator reduces the amount of fuel injected, resulting in a lean mixture.
A leak in the exhaust manifold or downpipe upstream of the bank 2 O2 sensor can introduce ambient air, skewing the sensor’s reading and triggering the code.
If the mass air flow sensor reports inaccurate air volume, the ECM miscalculates the required fuel, leading to a lean condition.
A software or hardware issue in the engine computer can cause incorrect fuel‑trim commands, but this is the least common cause and should be investigated only after other components are ruled out.
No. While a faulty PCM can set this code, it is rarely the cause. Most cases are traced to a sensor, fuel‑pressure problem, or an air leak.
Not always. The O2 sensor is a common culprit, but you should verify it is actually faulty and rule out other potential causes such as vacuum leaks or low fuel pressure first.
Yes. Unmetered air entering the intake from a leak creates a lean mixture that can trigger this code.
Start by inspecting the O2 sensor’s wiring and then look for obvious vacuum or exhaust leaks before moving to fuel‑pressure tests and sensor output checks.