engine codes
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From: Colorado
engine codes
All...I have an '03 Screw/5.4L/15140miles and recently had a problem. The SES light came on. I got home, pulled out the code reader and got codes 131 and 151=system running lean, left and right sides. Took it to the dealer, told him the codes and my thoughts being that the MAF had gone bad. They tested and agreed, HOWEVER, when they put the new MAF in and retested, the system would never stabilize the AF mixture,. now running rich! They told me to take it home since no one would be there on Saturday (inventory day) to work on it, and to watch it as it was running fine. The SES light came on again today, codes are for runnning rich left and right. The computer is supposed to be able to stabilize the lean/rich setting but doesnt seem to be. Any of you out there had a similar problem and know of "the" fix.
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Joined: Jun 2002
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From: Under the flightpath of old ORD 22R
Seems strange, but I don't see where the P0131 and P0151 codes refer to the MAFS.
The manual shows this as a Low Voltage out of range condition ( DTC excerpts from Service Manual included below ), and notes either Contaminated HO2S or crossed wiring on the HO2S.
Making teh assumption that you have not had to re-wire the HO2S harness, my guess would be that the HO2S is crapped up from a load of bad fuel, and either a) needs to be driven to empty, and replaced with good fuel
and / or
b) need to replace the O2 sensors 11 & 21. ( pass side and drivers side first HO2S ).
If the HO2S has a problem and cannot read the A/F mixture, then you will get swings in it. Replacing the first HO2S on both sides would be the first place to start in my book, considering how hard it would be to drain a whole tank of gas ( if it is still the same tank ) and dispose of ~ 25 gals of gas, and then refuel and start over.
Now the disclaimer, just because the Service Manual does not say that the MAFS is on the list of suspect items, does not mean that is cannot be that, but having already replaced it, and getting the same problem, could be an indication that this was not the problem child in the tree.
Try both HO2S next, clear the code, and if you haven't yet, run that tank as low as you can, and fuel at a different known brand name gas station ( remove the bottom of the tank farm drops, and a high traffic station probablly turns over the gas in the tanks quicker ).
Good Luck, let us know what happens.
DTC
P0151 - HO2S Sensor Circuit Out of Range Low Voltage (HO2S-21)
Description
See DTC P0131
DTC
P0131 - HO2S Sensor Circuit Out of Range Low Voltage (HO2S-11)
Description
The HO2S sensor is monitored for a negative voltage known as characteristic shift downward (CSD). If the sensor is thought to be switching from 0 volts to -1 volts during testing, the PCM will use this input and remain in fuel control.
Possible Causes
- Contaminated HO2S (water, fuel, etc)
- Crossed HO2S signal /signal return wiring
Diagnostic
The manual shows this as a Low Voltage out of range condition ( DTC excerpts from Service Manual included below ), and notes either Contaminated HO2S or crossed wiring on the HO2S.
Making teh assumption that you have not had to re-wire the HO2S harness, my guess would be that the HO2S is crapped up from a load of bad fuel, and either a) needs to be driven to empty, and replaced with good fuel
and / or
b) need to replace the O2 sensors 11 & 21. ( pass side and drivers side first HO2S ).
If the HO2S has a problem and cannot read the A/F mixture, then you will get swings in it. Replacing the first HO2S on both sides would be the first place to start in my book, considering how hard it would be to drain a whole tank of gas ( if it is still the same tank ) and dispose of ~ 25 gals of gas, and then refuel and start over.
Now the disclaimer, just because the Service Manual does not say that the MAFS is on the list of suspect items, does not mean that is cannot be that, but having already replaced it, and getting the same problem, could be an indication that this was not the problem child in the tree.
Try both HO2S next, clear the code, and if you haven't yet, run that tank as low as you can, and fuel at a different known brand name gas station ( remove the bottom of the tank farm drops, and a high traffic station probablly turns over the gas in the tanks quicker ).
Good Luck, let us know what happens.
DTC
P0151 - HO2S Sensor Circuit Out of Range Low Voltage (HO2S-21)
Description
See DTC P0131
DTC
P0131 - HO2S Sensor Circuit Out of Range Low Voltage (HO2S-11)
Description
The HO2S sensor is monitored for a negative voltage known as characteristic shift downward (CSD). If the sensor is thought to be switching from 0 volts to -1 volts during testing, the PCM will use this input and remain in fuel control.
Possible Causes
- Contaminated HO2S (water, fuel, etc)
- Crossed HO2S signal /signal return wiring
Diagnostic