My mothers Enclave just started having 'running issues' as she put it yesterday. The way she was describing it, it sounded kind of like a torque converter partially locking while stopped, because she said the issue went away when she got moving, but when I got there today to see what I could see, I got the list of DTCs in the title (P0131 P0137 P0151 P0157 P0171 P0174). Long Term and Short Term fuel trims get pegged to the roof.
So I went over the engine the best I could, checking for obvious vacuum leaks, but I couldn't find anything obvious. All points that would affect both banks appear solid. I used brake clean to try and find any leaks, no dice.
Data shows B1S1 starts low voltage (10-20mv) then appears to start switching normally. B1S2 goes high (700-800mv) at about the same time, which I believe is normal as if the cats are working right, you shouldn't see the rich/lean switching post cat, and both B2 sensors stay low, less than 100mv. It seems the odds of all four sensors going out the same way at the same time are low, and the O2 sensor DTCs weren't history, and both 'Last Test' and 'This ignition cycle' show 'Passed'. I don't know if the low readings are accurate and it really is super lean despite the high fuel trims, fuel rail pressure appears to be holding between 500-600PSI, which I gather is normal for GDI engines. MAF airflow runs around 3 g/s at idle.
If there was a vacuum leak between the intake manifold and a head, that would most likely only show up for one bank. For one to affect both banks, it would have to be in the upper intake manifold or between there and the MAF. But I can't find any.
Given that I can't find any obvious vacuum leaks, my thoughts are going to either a failed/failing MAF or an ECM. Given that the Long terms peg to +34 pretty fast and the short terms peg to 40, that would suggest a fairly large vacuum leak that would probably be pretty noticeable.
Has anyone seen this list of codes or have any thoughts on something I may have missed?
So I went over the engine the best I could, checking for obvious vacuum leaks, but I couldn't find anything obvious. All points that would affect both banks appear solid. I used brake clean to try and find any leaks, no dice.
Data shows B1S1 starts low voltage (10-20mv) then appears to start switching normally. B1S2 goes high (700-800mv) at about the same time, which I believe is normal as if the cats are working right, you shouldn't see the rich/lean switching post cat, and both B2 sensors stay low, less than 100mv. It seems the odds of all four sensors going out the same way at the same time are low, and the O2 sensor DTCs weren't history, and both 'Last Test' and 'This ignition cycle' show 'Passed'. I don't know if the low readings are accurate and it really is super lean despite the high fuel trims, fuel rail pressure appears to be holding between 500-600PSI, which I gather is normal for GDI engines. MAF airflow runs around 3 g/s at idle.
If there was a vacuum leak between the intake manifold and a head, that would most likely only show up for one bank. For one to affect both banks, it would have to be in the upper intake manifold or between there and the MAF. But I can't find any.
Given that I can't find any obvious vacuum leaks, my thoughts are going to either a failed/failing MAF or an ECM. Given that the Long terms peg to +34 pretty fast and the short terms peg to 40, that would suggest a fairly large vacuum leak that would probably be pretty noticeable.
Has anyone seen this list of codes or have any thoughts on something I may have missed?
