How to change fuel injector bank one? My son's 97 mercury mystique to thorwing a P1131 code for the fuel injector in bank one. Also throwing a P0133 for the O2 sensor. How do I replace the fuel injector myself and are the 2 P codes linked together?? Thanks, Felix

Try cleaning the MAF sensor first, then check for any unmetered air getting into throttle body (leaks in intake hose). Bank 1 is the driver's side of the engine (or front on FWD) and bank 2 is the passenger side.

P1131 - Lack Of HO2S Switch - Sensor Indicates Leanhttp://engine-codes.com/p1131.htmlForum CodePossible causes- Vacuum leak affecting bank 1 only
- Fuel injector problem bank 1
- Check for cylinder misfire on bank 1
- Engine mechanical condition
- Faulty O2 sensor. Symptoms- Engine Light ON (or Service Engine Soon Warning Light)P1131 Description A Heated Exhaust Oxygen (HO2S) sensor indicating lean at the end of a test is trying to correct for an over-rich condition. The test fails when the fuel control system no longer detects switching for a calibrated amount of time.

• Bank 1 sensor 1 O2 Sensor. Also with this or they are very known for an intake gasket leak. Make sure to check your vacuum hoses first.
• First check for vacuum leak from a hose. If none are found switch that top O2 Sensor (upstream) If this persists after all that you may have an intake vacuum leak.

Regards, Tony

P1131 is "Lack of H02S-1,1 Switch, Sensor indicates lean" I'd say you've got a bad Heated Oxygen Sensor at Bank 1, Sensor 1.

H40 DTCs P1131, P1132, P1151 AND P1152: UPSTREAM HO2S NOT SWITCHING. DTC P1130: FUEL SYSTEM NOT SWITCHING AT FUEL TRIM (RICH OR LEAN)

Diagnostic Trouble Codes (DTCs) P1131 bank 1 (Cylinder 1) and P1151 bank 2 indicate the fuel/air ratio is correcting rich for an overly lean condition. The HO2S voltage is less than 0.45 volt. DTCs P1132 bank 1 (Cylinder 1) and P1152 bank 2 indicate the fuel/air ratio is correcting lean for an overly rich condition. The HO2S voltage is greater than 0.45 volt.
DTC P1130 and P1150 indicate the fuel control system has reached maximum compensation for a lean or rich condition and the HO2S is not switching.
DTC/HO2S Reference List

• HO2S-11 = DTCs P1131, P1132 and P1130
• HO2S-21 = DTCs P1151, P1152 and P1150
Possible causes:
Fuel system

• Excessive fuel pressure.
• Leaking fuel injector(s).
• Leaking fuel pressure regulator.
• Low fuel pressure or running out of fuel.
• Contaminated fuel injector(s)
• Vapor recovery system
Induction system

• Air leaks after the MAF.
• Vacuum leaks (vacuum lines and gaskets).
• Restricted air inlet.
• PCV system.
• Improperly seated engine oil dipstick.
EGR System

• Leaking gasket.
• Stuck open EGR valve.
• Leaking diaphragm.
Base engine

• Oil overfill.
• Cam timing.
• Cylinder compression.
• Exhaust leaks before or near the HO2Ss.
• Check intake air system for leaks, obstructions and damage.
• Check air cleaner element, air cleaner housing for blockage.
• Verify integrity of the PCV system.
• Check for vacuum leaks.

P1131 -1. Misfire on bank 1
2. Vacuum leak affecting bank 1
3. Fuel injector problem bank 1

P1130 - 1. Fuel pressure high or low
2. MAP sensor dirty/defective
3. Vacuum leak on engine
4. Leaking fuel injector or fuel pressure regulator

Sounds like your mass air flow sensor. It measures the amount of air going to the throttle body and the injectors should spray the rquired amount, so the computer thinks there isn't much air therfore it runs lean,,, sending the po171 code. Can be a quick fix.Get the part and change it in the parking lot.

check fuel pressure . fuel pump likely going bad

P1131 bank 1 indicates the fuel/air ratio is correcting rich for an overly lean condition.
Diagnostic Trouble Codes (DTCs) P0133 and P0153 indicates the response rate of the upstream HO2S(s) is below some calibrated window. The test measures the HO2S amplitude and output frequency. This is accomplished by superimposing a 1.5 to 2.5 Hz square wave over Lambse. The HO2S switching is monitored during this time to see if the calibration limit is met. P0133 is also bank 1.
Although these codes could be caused by several things such as vacuum leaks,fuel contamination,exhaust leaks,miss-fires,etc. Since it is localized on only bank one I would replace that front(upper in the exhaust to back cylinder head) 02 sensor and see if that did not correct my concern.

Based on what the tech manuals say I would change the DPFE sensor for the EGR Valve, careful not to tear the special silicone rubber hoses that go to it from the exhaust, as a Ford dealer tech I saw these codes allot, and the DPFE sensor was almost always the issue or the hoses going to it.