I'm experiencing a P1175 diagnostic trouble code on my 2008 Chevrolet Silverado 2500HD. What could be causing this issue? The truck has only the P1175 code registered, and I'm looking for accurate troubleshooting steps based on real-world experiences and technical specifications.
I also get P1175 on my 2008 Silverado 2500HD. It's occurred four times now. The unusual part is that my son lives in Denver (6,000 feet above sea level), where regular fuel is 85 octane. We leave early at 6:00 AM and drive east at 80 MPH until we reach Nebraska for gas. After refueling with 87-octane fuel, we return to I-80 and notice the check engine light comes on. I reset the code and drove another three months before it returned. This pattern suggests a possible link between altitude (air density), temperature, or fuel octane—either individually or in combination.
This is an interesting case — and I didn't know that 85-octane was standard at high altitudes. Why would that be? Anyway, I'll have to investigate further. Could you clarify which engine your truck has? Is it stock configuration? Are there any other diagnostic codes present? What exactly does P1175 mean — can you confirm the code? Does your OBD2 scanner support live data such as fuel trim values or fault counts? A fuel system treatment like Techron or SeaFoam might help, especially if the issue is related to fuel delivery.
85-octane fuel — I didn't realize it was standard at high elevations. I’ve used premium fuel while towing heavy loads through mountainous terrain and haven’t noticed a significant difference in mileage or performance (neither is great with over 8,000 lbs at 10,000 feet anyway). The trailer isn’t involved in this current issue. My truck is a 2008 Silverado 2500HD with the stock 6.0L V8 engine. Only P1175 appears in the diagnostic logs. I’m currently using TouchScan on my laptop to generate live data and logs. I’ll try fuel treatment (like SeaFoam) during my next trip west (likely March). Any suggestions for logging duration or format? Will a 4-hour log fit on my hard drive?
I believe P1175 points to a fuel injector issue rather than being directly caused by lower octane — though the octane level might amplify an existing problem. The long highway runs followed by idle stops could be stressing the injectors. SUGGESTION: Clean the fuel injectors or perform a diagnostic test using AFIT CH-47976. Diagnostic tips to consider: > Is this B2S1 an OEM oxygen sensor? > Monitor misfire current counters or misfire graphs to identify which cylinder is causing imbalance. Technical note: The Fuel Trim Cylinder Balance diagnostic detects air/fuel ratio imbalances between engine banks by analyzing the pre-catalyst (HO2S) signal’s frequency and amplitude over a set period. An imbalance occurs when multiple samples show consistently higher accumulated voltage than expected.
Update: I added SeaFoam before leaving Chicago and used mid-grade fuel (89 octane). No check engine light came on during the trip. On my second journey, I didn’t use any cleaner but switched to better-quality fuel — still no MIL. Now I’m wondering whether it was the fuel treatment or the higher-octane fuel that resolved the issue. Going forward, I’ll simply stick with premium fuel.
What does the owner’s manual say about fuel octane at high altitudes? I have no experience with this 85-octane standard — it sounds like you're testing real-world conditions. My two cents: SeaFoam works well, but try switching to 85-octane fuel first and see what happens. If any local GM technicians provide insights, please share them with the community.
Fuel injectors are a common suspect for P1175. If you've already used injector cleaner in the fuel tank, consider moving to a more direct solution like professional fuel injector cleaning or testing.