1999 Codes

99 with 62,000 miles.

I had an intermittent problem (happened twice) with the car not accelerating properly and at times almost stalling. No CEL though. Car had been working fine for two weeks than CEL
Comes on. I get P1129, P0154, P1127.

Is it reasonable to assume this was causing my accelerating problems? Is my best course of action to replace all the o2 sensors? Would sensors on both sides go out at the same time? Anything else I should do or replace?
Did the AOS cap test and that seems ok, but I am open to all ideas or suggestions.


Thanks!

Quote
keithl
99 with 62,000 miles.

I had an intermittent problem (happened twice) with the car not accelerating properly and at times almost stalling. No CEL though. Car had been working fine for two weeks than CEL
Comes on. I get P1129, P0154, P1127.

Is it reasonable to assume this was causing my accelerating problems? Is my best course of action to replace all the o2 sensors? Would sensors on both sides go out at the same time? Anything else I should do or replace?
Did the AOS cap test and that seems ok, but I am open to all ideas or suggestions.


Thanks!

the engine is being fed an overly rich mixture.

Fuel pressure comes under suspicion or one (or since the error codes come from both banks) two injectors (one on each bank) may be leaking.

I'd work on the P1127/P1129 error codes first before worrying about one O2 sensor error code.

There are several tests one that involves checking fuel pressure at the fuel pressure test point on a fuel rail. This test calls for connecting a fuel pressure gage using the Porsche tool P378A and adapter 9559 to the test port then activating the fuel pump (a bridging relay can be used). The fuel pump should operate and fuel pressure should be (with engine off) 55psi +/- 3psi (3.8 bar +/- 0.2 bar) and with engine running 48psi +/- 3psi (3.3 bar +/- 0.2 bar). The fuel pressure test point cap must be replaced after this test.

Another test has the vacuum line from teh fuel pressure regulator removed and connected to a vacuum/pressure gage. Then the engine is started and the vacuum (pressure) should read between 6 to 9 psi (0.4 to 0.6 bar).

If one sensor bad I'd advise you to replace both. If you replace one that means one bank has a new sensor while the other bank as an old/aged one. This may result in an artifical (due to the age of one sensor and the newness of the other sensor) imbalance between cylinder banks.

At 62K miles you've gotten quite a bit of life/usefulness out of the sensors.

Sincerely,

MarcW.

Quote
MarcW

Quote
keithl
99 with 62,000 miles.

I had an intermittent problem (happened twice) with the car not accelerating properly and at times almost stalling. No CEL though. Car had been working fine for two weeks than CEL
Comes on. I get P1129, P0154, P1127.

Is it reasonable to assume this was causing my accelerating problems? Is my best course of action to replace all the o2 sensors? Would sensors on both sides go out at the same time? Anything else I should do or replace?
Did the AOS cap test and that seems ok, but I am open to all ideas or suggestions.


Thanks!

the engine is being fed an overly rich mixture.

Fuel pressure comes under suspicion or one (or since the error codes come from both banks) two injectors (one on each bank) may be leaking.

I'd work on the P1127/P1129 error codes first before worrying about one O2 sensor error code.

There are several tests one that involves checking fuel pressure at the fuel pressure test point on a fuel rail. This test calls for connecting a fuel pressure gage using the Porsche tool P378A and adapter 9559 to the test port then activating the fuel pump (a bridging relay can be used). The fuel pump should operate and fuel pressure should be (with engine off) 55psi +/- 3psi (3.8 bar +/- 0.2 bar) and with engine running 48psi +/- 3psi (3.3 bar +/- 0.2 bar). The fuel pressure test point cap must be replaced after this test.

Another test has the vacuum line from teh fuel pressure regulator removed and connected to a vacuum/pressure gage. Then the engine is started and the vacuum (pressure) should read between 6 to 9 psi (0.4 to 0.6 bar).

If one sensor bad I'd advise you to replace both. If you replace one that means one bank has a new sensor while the other bank as an old/aged one. This may result in an artifical (due to the age of one sensor and the newness of the other sensor) imbalance between cylinder banks.

At 62K miles you've gotten quite a bit of life/usefulness out of the sensors.

Sincerely,

MarcW.

Thanks. Do you think the fuel pump could be to blame?

pressure regulator should limit the fuel pressure if the fuel pump was producing too much pressure.

Which it most likely is doing. The fuel pump must have some margin of flow and pressure so it is not running at its max. rated pressure and volume constantly. Remember the fuel pump has so supply the engine with sufficient fuel from hot idle to the engine running flat out at redline, and possible at this speed for a long time. Well, as long as the driver can drive the car flat out. In testing (and on the track) these cars are driven pretty fast for long periods of time and over some distances.

Sincerely,

MarcW.

If my memory serves me (and it isn't doing that too well lately) I had an overly rich mixture that was caused by a faulty o2 sensor. Shouldn't you get the sensors corrected as they feed data back to the computer to then change mixture?

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Bruce In Philly (175K+)
If my memory serves me (and it isn't doing that too well lately) I had an overly rich mixture that was caused by a faulty o2 sensor. Shouldn't you get the sensors corrected as they feed data back to the computer to then change mixture?

That would be the nice if that was the cause. It doesn't seem to be the AOS.

does not fail in a way that results in an engine being fed too much fuel. If the AOS affects the air fuel mixture it does by leaning it out and causing the DME to possibly reach its enrichment limit. Now there can be a curious side effect in that teh AOS leak can be a large one at idle, but at higher rpms drop off to near nothing. If the DME richens the mixture to compensate for a failing AOS and just before it reaches its enrichment threshold if the driver takes off and the engine speed increases and remains elevated the DME then will go the other way and undo its enrichment and instead of course lean the mixture out. It is possible the DME might reach its lean limit under some conditions. (I note this happened when my Boxster's oil cap was leaking. Sometimes the error codes pointed to an air leak but once in a while would point to an overly rich condition. I took this to be the MAF but it turned out to be a leaking oil filler tube cap.)

Anyhow, my info is that the O2 sensor does not fail in such a way that causes it to add a bias to its voltage output. The usual failures are the sensor stops providing readings (the sensor voltage flatlines at around 0.45V) or the sensor simply can't react fast enough to the DME's constant swinging of the air fuel mixture from overly rich to lean. I might add the swings are very tiny.

Anyhow if the O2 sensors exhibits any of the above behavior this will have the DME issuing the appropriate O2 sensor related error code(s).

I might add that the sensors must be active and working properly as determined by the DME before it will generate a P1127 error code.

My references do not even list the O2 sensor as one of the possible causes of a P1127/P1129 error. The possible causes are: MAF (incorrect signal), fuel pressure too high, fuel injector leaking, or EVAP canister purge valve open.

Since the MAF can play a role one possible way to eliminate the MAF is to disconnect it the wiring harness connector, clear the error codes (resets the learned fuel trims among other things) to their defaults, then drive the car normally. The car must be driven a considerable distance around 30 miles to hopefully parallel close enough a drive cycle that has the DME able to verify all systems are working and if the MAF is not the cause of the P1127/P1129 error codes to log them so you know.

Sincerely,

MarcW.



Edited 1 time(s). Last edit at 07/14/2011 02:01PM by MarcW. (view changes)

Quote
MarcW
does not fail in a way that results in an engine being fed too much fuel. If the AOS affects the air fuel mixture it does by leaning it out and causing the DME to possibly reach its enrichment limit. Now there can be a curious side effect in that teh AOS leak can be a large one at idle, but at higher rpms drop off to near nothing. If the DME richens the mixture to compensate for a failing AOS and just before it reaches its enrichment threshold if the driver takes off and the engine speed increases and remains elevated the DME then will go the other way and undo its enrichment and instead of course lean the mixture out. It is possible the DME might reach its lean limit under some conditions. (I note this happened when my Boxster's oil cap was leaking. Sometimes the error codes pointed to an air leak but once in a while would point to an overly rich condition. I took this to be the MAF but it turned out to be a leaking oil filler tube cap.)

Anyhow, my info is that the O2 sensor does not fail in such a way that causes it to add a bias to its voltage output. The usual failures are the sensor stops providing readings (the sensor voltage flatlines at around 0.45V) or the sensor simply can't react fast enough to the DME's constant swinging of the air fuel mixture from overly rich to lean. I might add the swings are very tiny.

Anyhow if the O2 sensors exhibits any of the above behavior this will have the DME issuing the appropriate O2 sensor related error code(s).

I might add that the sensors must be active and working properly as determined by the DME before it will generate a P1127 error code.

My references do not even list the O2 sensor as one of the possible causes of a P1127/P1129 error. The possible causes are: MAF (incorrect signal), fuel pressure too high, fuel injector leaking, or EVAP canister purge valve open.

Since the MAF can play a role one possible way to eliminate the MAF is to disconnect it the wiring harness connector, clear the error codes (resets the learned fuel trims among other things) to their defaults, then drive the car normally. The car must be driven a considerable distance around 30 miles to hopefully parallel close enough a drive cycle that has the DME able to verify all systems are working and if the MAF is not the cause of the P1127/P1129 error codes to log them so you know.

Sincerely,

MarcW.

Thanks a lot for the info.

I had a similar problem 1128/1130 code which is the computer maxing out trying to over come a lean condition at idle. I had this code for a while, it turned out to be a piece missing in my air box which allowed extra air to enter the motor.The computer responded by adding fuel and turning on 1128/1130 code light. Your problem may be the opposite you may have an air restriction which will cause you to run rich (like an old fashion choke ) check the intake to make sure that some kid did not stuff his McDonald's wrapper into your air vent. or that your air filter is plugged.

Thanks, I'll do that!

Update. I had all of the tests performed and everything checked out fine. Weird, I know I didn't imagine the problems or the check engine light. The car is driving fine now. Oh well.

the light and codes will be back. Sometimes -- I've found -- it can take a bit of driving to reproduce the driving conditions that give the DME the chance (and the time) to detect the problem and set the error codes and light the CEL.

Sincerely,

MarcW.

I keep getting a P1123 code (only), and have changed out passenger side O2's and all of the vacuum parts (canister, electronic valve, metal valve and all of the hoses). Any ideas on this one? '99 2.5L with 86K miles...

one would think this would make the error for the other bank appear too. However, sometimes one bank gets to the limit before the other and one code is all that is present, though the other might be pending.

Could be the vacuum line at the fuel pressure regulator.

Or a leaking injector.

How much diagnostics are you willing to do?

Sincerely,

MarcW.