P0148 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Causes

Common causes for this code include:

• Faulty fuel pump or high-pressure regulator 
• Leaking or restricted fuel injector(s) 
• Low system voltage which may be a result of a bad alternator 
• MAF sensor concern on GDI
• Bad ECM (Engine Control Module) 
• Restricted fuel line
• Open, short, or corroded wiring in the electrical harness causing interruption between power supply and components causing insufficient voltage 
• Incorrect PCM calibration 
• The fuel filter has been severely restricted.
• Vacuum leaks internally in the engine compartment, vacuum lines not connected to engine components, faulty engine control sensors

Symptoms

The symptoms of a P0148 code are:

• The check engine light will come on 
• Hard or no start during cold weather 
• Engine stalls while driving or when coming to a stop 
• Poor acceleration and idle quality
• Black smoke from the tailpipe
• Increased fuel consumption

Diagnosis

To diagnose a P0148 DTC code, an automotive technician would:

1. Check the fuel pressure and ensure it is within specifications.
2. Check for vacuum leaks in the intake manifold, hoses, wiring harnesses, etc., with a leak tester to see if they are causing any large or small vacuum leaks.
3. Ensure there is no dirt or debris blocking airflow through the MAF sensor. 
4. Test all system voltage components using an analyzer to ensure that there are no low voltages present between ECM power supply circuits and sensors/components on GDI engine(s). This can be done by checking each relay for sufficient voltage drop when activated by operating light switches, applying probes directly across relay terminals, or with an inductive ammeter placed around each wire in question while operating the engine on a test bench.
5. Verify that the PCM (Powertrain Control Module) is calibrated correctly by checking the calibration stored in the module and comparing it against another known good ECM. This can be done by checking each calibration with an analyzer or determined by checking fuel injection timing, air flow rate, throttle position and other engine operating parameters.

Common mistakes

The following are common mistakes when diagnosing the trouble code P0148:

Not checking the fuel pressure to ensure it is within specifications before diagnosing.

Not checking for vacuum leaks in hoses, wiring harnesses, etc., with a leak tester.

Skipping steps and not testing all system voltage components using an analyzer to determine if there are low voltages present between ECM power supply circuits and sensors/components on GDI engine(s). 

Improper placement of inductive ammeter around each wire when performing step 4.

Skipping step 5 by just comparing calibration stored in the module with another known good ECM without first verifying that the PCM has been calibrated correctly.

Relying solely on a scan tool data list or snapshot data which can be misleading because there has been reported variances of the trouble code P0148.

Not checking for fuel pressure checking all causes in step 2 before replacing any parts, especially after diagnosing a failed or faulty ECM (Powertrain Control Module).

How serious is this?

A car with a P0148 trouble code will drive just fine, but the engine will have lost some power and efficiency due to not receiving enough fuel to reach all its components. 

If this code is set with several other codes in a GDI (Gasoline Direct Injection - car with PFI or Port Fuel Injection) engine, it can cause the check engine light to blink continuously. This means that resetting the code(s) isn't fixing all of them and further diagnosis is needed. 

The vehicle may be safe to operate but performance wise, it won't be operating to its full potential. A misfiring engine can also damage catalytic converters, so if the problem is ignored long enough, there might come a time when replacing them becomes necessary and can end up being quite costly in that case.

What repairs can fix the code?

The following are solutions that may fix this problem:

Clearing the code and retesting to see if it returns. If it does, go through all the other potential solutions until the engine starts running properly again.

If there are no vacuum leaks in hoses, wiring harnesses, etc., with a leak tester or dirt or debris blocking airflow through the MAF sensor, then replacing either one of these parts could fix this P0148 trouble code. 

Replacing fuel injectors could also be another solution to look into depending on which cars/engines are having problems with P0148.

Resetting or servicing (flashing) PCM (Powertrain Control Module). 

Checking calibration stored in the module against another known good module may also help pinpoint where the problem lies.

Testing fuel pressure to ensure it is within specifications before diagnosing.

Related codes

A P0148 is related to and may be accompanied by the following codes: 

P0141, P0151, P0152, P0156, P0158, P0160, P0230, P0236, P0237, or P0238

How much does it cost to fix the P0148 code?

The repair cost of a P0148 code is $100 - $500 depending on the type of car and whether there are any additional codes present. 

However, it may require replacing fuel injectors, PCM (Powertrain Control Module), MAF sensor and/or recalibrating based on testing results. A new O2 sensor might also be required if that is causing the problem. That would run anywhere from about $150 to $800 depending on which cars require replacement and how many sensors need replacing. It might be worth it to get a proper estimate so repairs can get done correctly the first time.

Conclusion

In conclusion, the P0148 is a trouble code that means there is a problem with the fuel level between ECM power supply circuits and sensors/components. A P0148 trouble code may be set along with several other codes, which can cause the check engine light to blink continuously. Symptoms of this trouble code might include the vehicle running fine, but not being as efficient or powerful as it should be. The problem can be fixed by checking for vacuum leaks, replacing fuel injectors, testing fuel pressure, recalibrating PCM modules and resetting them if necessary.