Mazda CX-7 P2177 and P2187

I have a Mazda CX-7, 2.3L, Turbo, 2009, with trouble codes P2177 and P2187, long term fuel trim is 20 all the time, ilde or off idle, short term fuel trim is 18 and higer. I already verified for vacuum leaks, as well as for fuel pressure, both are within specs. Also cleaned MAF, but didn't make any difference.

Any suggestions ?

Thank you

Hey JesusMercado! For our info, P2177 is defined as "System Too Lean Off Idle Bank 1" and P2187 is "System Too Lean at Idle B1", correct? That's what Google tells me, anyway, just making sure.

My first thought is that the upstream air/fuel ratio sensor has failed, and is falsely reporting a lean condition. When driving, does the engine feel like it's low on power? If not, that would suggest the lean condition IS false, and that the PCM is actually overfueling the engine. If it is low on power, then the lean condition probably does exist.

If you have access to Global OBD scan data, then it'll be very easy to track down a lying air/fuel ratio sensor by comparing the upstream sensor against the downstream. At idle, look at the Bank 1 Sensor 1 O2 Current in mA and the Bank 1 Sensor 2 O2 voltage. For reference, the upstream sensor will show positive current if the exhaust is lean, and negative current if it's rich. The downstream sensor works like a conventional O2, with low voltage representing lean, and high representing rich. Here's an example of what a working upstream sensor looks like, off an '08 Mazda 6.





If you see the upstream sensor showing lean, but the downstream sensor showing rich, then it's likely that the upstream sensor is lying. If they BOTH show lean, then it's probably telling the truth, and we can go further into a fuel delivery problem.

For more info on air/fuel ratio sensors, we've got a thread going right here . Paul also has several different videos out demonstrating this kind of rationality testing:

Thank you Tyler,
I took a look with the scanner this morning after driving 10 miles, getting the following:
Oxygen sensor voltage bank 1 sensor 2 = 0.905 volts
Current Sensor 1 = -0.20 mA

5 hours after I did a double check ( after warming up) getting the following:
Oxygen sensor voltage bank 1 sensor 2 = 0.020 volts
Current Sensor 1 = -0.23 mA

Then I drove the car for about 10 minutes in the town, getting the following:
Oxygen sensor voltage bank 1 sensor 2 = 0.215 volts
Current Sensor 1 = -0.14 mA

LTFT was 20.3 all the time in all of the tests

Would that confirm a bad upstream oxygen sensor ?

Thank you

JesusMercado wrote: Thank you Tyler,
I took a look with the scanner this morning after driving 10 miles, getting the following:
Oxygen sensor voltage bank 1 sensor 2 = 0.905 volts
Current Sensor 1 = -0.20 mA

5 hours after I did a double check ( after warming up) getting the following:
Oxygen sensor voltage bank 1 sensor 2 = 0.020 volts
Current Sensor 1 = -0.23 mA

Then I drove the car for about 10 minutes in the town, getting the following:
Oxygen sensor voltage bank 1 sensor 2 = 0.215 volts
Current Sensor 1 = -0.14 mA

LTFT was 20.3 all the time in all of the tests

Would that confirm a bad upstream oxygen sensor ?

Thank you

Thanks for getting back to me with those readings! Kinda weird that the upstream air/fuel ratio sensor always reads about -.2 mA... Did this reading fluctuate during your drive? The negative current indicates rich, which doesn't account for your lean trims, I just want to know the sensor is capable of reacting to changing fuel mixtures. What were the short term trims doing while driving? Staying high as before?

I think we can clear the air/fuel ratio sensor for now and go on to other possible issues. Any possibility that E85 fuel got pumped into the tank? That'd absolutely cause a lean condition. If you're confident there are no air leaks, and the fuel pressure is in spec, then I'd suggest revisiting the MAF. I see that you cleaned it already, but it could still be skewed anyway.

We can do a quick test of the MAF by watching Calculated Engine Load during a WOT run through first gear and into second. You'll want to have the data list narrowed down to Engine Speed, Airflow Rate, Calculated Engine Load, Absolute Engine Load and the upstream air/fuel sensor current in mA. We want the Calculated Load to go over 90% and the air/fuel sensor current to go negative during the run. Low Load and positive sensor current would point towards a misreporting MAF sensor.

Hello
upstream air/fuel ratio sensor fluctuates while driving, in some of the cases can get positive current readings. SRFT fluctuates as well while driving but most of the time is positive, just when driving very slow, like in a marking lot, the readings change to negative value, around -15.

I did the run that you recommended to test the MAF getting the following:
Calculated load value: 66.3%
Engine Speer: 4071 rpm
MAF air flow: 92.88 g/s
Current sensor 1: -0.36 mA
Absolute load value: 98.4%

Also did a run at low load value getting the following:
Calculated load value: 23.9%
MAF air flow: 6.06 g/s
Current sensor 1: -0.28 mA
Absolute load value: 25%

I thing is going to be a misreporting MAF, so I´m ordering a new one from rockauto.com.

I had a recent run in with these same codes on a 2009 CX-7 a couple months ago. I don't remember how these Air/Fuel sensor signals work (what the signal does when the exhaust is rich/lean), but I suggest that you force the system rich and lean while monitoring the Air/Fuel sensor PIDS to see how/if it responds. In my case the codes were accompanied by a violent surge on part throttle acceleration and the Air/Fuel sensor signal was erratic during the surging (switching rich/lean). I confirmed that the sensor was faulty and replaced it. I road tested the vehicle, verified the repair and returned the vehicle to the customer.

2 weeks later the vehicle returned with the same codes... and the same problem. What I found was TSB 01-009/13 for codes P2177 and P2187 which calls for a "short cord" installation between the sensor and the PCM due to brake fluid contamination of the harness. I verified the harness was in fact shorted between the Air/Fuel sensor circuits per the TSB and installed the short cord. I also had to replace the sensor again (as the short in the harness had somehow damaged the new sensor). Installing the short cord was a PITA but the vehicle has not been back. This might not be your problem but if you find that the Air/Fuel ratio sensor is suspect or faulty, I would recommend checking for shorting between the sensor circuits with the sensor and PCM disconnected.

JesusMercado wrote: I did the run that you recommended to test the MAF getting the following:
Calculated load value: 66.3%
Engine Speer: 4071 rpm
MAF air flow: 92.88 g/s
Current sensor 1: -0.36 mA
Absolute load value: 98.4%

I thing is going to be a misreporting MAF, so I´m ordering a new one from rockauto.com.

Thanks for the results. Was this the highest Calculated Load you could get out of it? If so, definitely an issue. I dunno what kind of airflow rate your engine is supposed to have, but less than 100 g/s sounds low for a forced induction engine. The Absolute Load also sounds low. I'd expect 120% or better at WOT.

What I found was TSB 01-009/13 for codes P2177 and P2187 which calls for a "short cord" installation between the sensor and the PCM due to brake fluid contamination of the harness.

I saw the same TSB! I didn't give it much thought since it seems like the AFR sensor is working at the moment, but I suppose it could be more intermittent?

Thank you, that's a good point I will check the harness for the air/fuel sensor just to make sure it is till working properly.