P0173
Fuel Trim Malfunction (Bank 2)
The appearance of the standard OBD2 trouble fault code P0173 is an indicator that your vehicle ECU triggered a threshold alert for "Fuel Trim Malfunction (Bank 2)". Understanding the root component breakdown helps avoid expensive diagnostic fees.
Driver's Summary
A P0173 fault code points directly to a problem with fuel trim malfunction (bank 2) that the ECM has confirmed over multiple drive cycles. In practice, this fault causes decreased fuel economy, check engine light, rough idle. This condition is classified as high severity. Prompt diagnosis is essential to prevent cascading damage to related components.
Symptoms
Decreased fuel economy, check engine light, rough idle
Common Causes
- Vacuum leak specific to Bank 2 intake manifold
- Faulty fuel injectors on Bank 2
- Failed Bank 2 O2 sensor
- Exhaust leak before the O2 sensor
How to Fix
- 1 Inspect Bank 2 intake gaskets
- 2 Clean or replace Bank 2 fuel injectors
- 3 Replace upstream O2 sensor
- 4 Repair exhaust manifold leak
Technical Explanation
The ECM detects code P0173 by continuously monitoring the relevant sensor circuit against calibrated threshold values stored in its non-volatile memory. The module measures the voltage return on the 5V reference circuit, comparing it to the expected signal envelope at current engine load and RPM. A deviation greater than the calibrated threshold — typically ±10% outside the normal operating window — flags the fault. The MIL illuminates after the fault is confirmed on two consecutive drive cycles, and the freeze frame data captured at first detection is stored in the PCM's memory for diagnostic reference.
Is It Safe to Drive?
Driving with an active P0173 fault risks accelerating damage to vacuum leak specific to bank 2 intake manifold and related components. The longer the fault persists, the more expensive the eventual repair becomes — what starts as a sensor or solenoid issue can escalate to major mechanical failure.
Mechanic's Pro Tip
For P0173, always perform a smoke test before replacing any parts — unmetered air from a cracked intake boot, split hose, or failed gasket is the root cause in the majority of lean fault cases and costs almost nothing to fix. After any repair, clear the code and watch short-term fuel trim (STFT) live on a scan tool; it should recover to within ±5% at idle within 2–3 minutes if the vacuum leak is truly resolved.
Related Fault Codes
Frequently Asked Questions
What does OBD2 code P0173 mean?
OBD2 code P0173 refers to Fuel Trim Malfunction (Bank 2). The appearance of the standard OBD2 trouble fault code P0173 is an indicator that your vehicle ECU triggered a threshold alert for "Fuel Trim Malfunction (Bank 2)". Understanding the root component breakdown helps avoid expensive diagnostic fees.
What are the most common symptoms of DTC P0173?
Drivers experiencing code P0173 typically report: Decreased fuel economy, check engine light, rough idle.
Is it safe to drive with trouble code P0173 active?
Driving with an active P0173 fault risks accelerating damage to vacuum leak specific to bank 2 intake manifold and related components. The longer the fault persists, the more expensive the eventual repair becomes — what starts as a sensor or solenoid issue can escalate to major mechanical failure.
How much does it cost to fix code P0173?
The estimated repair cost for P0173 ranges from $100 to $800 USD. Intake gaskets: $300 - $600; Injectors: $200 - $500
Intake gaskets: $300 - $600; Injectors: $200 - $500
Need Professional Diagnostic Assistance?
Always verify sensor signals and wiring integrity with an OBD2 scanner before purchasing replacement parts.
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