OBD-II Code
P1108
Severity
Not yet reviewed
Nobody on our side has assessed this code yet, so we are not going to guess at how serious it is.
Can you drive it
We cannot say
Treat it as unknown until a shop reads it with live data. If the check-engine light is FLASHING, stop driving as soon as it is safe to — that means an active misfire, whatever the code.
Indicative cost (USD)
$0–$650
From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
$0 (relearn/recalibration after altitude change) to $650 (intake manifold gasket replacement on an LS truck).
P1108 is GM's BARO-to-MAP Sensor Comparison Too High — at key-on, the ECM compares the barometric pressure reading (from a discrete BARO sensor on older platforms, or from the MAP sensor sampled at KOEO on newer ones) against the MAP reading and looks for them to agree within a tight window (typically within 0.5V of each other since both are seeing atmospheric pressure at key-on).
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then follow the diagnostic notes further down this page, in the order they are written.
They are written in the order a shop works this code, cheapest checks first. Where they name a component, inspect its wiring and connector before replacing it.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Read the full diagnostic procedureP1108 is GM's BARO-to-MAP Sensor Comparison Too High — at key-on, the ECM compares the barometric pressure reading (from a discrete BARO sensor on ol…
P1108 is GM's BARO-to-MAP Sensor Comparison Too High — at key-on, the ECM compares the barometric pressure reading (from a discrete BARO sensor on older platforms, or from the MAP sensor sampled at KOEO on newer ones) against the MAP reading and looks for them to agree within a tight window (typically within 0.5V of each other since both are seeing atmospheric pressure at key-on). When they disagree by more than the threshold and MAP is reading HIGHER than BARO, the ECM sets P1108. This is almost always either a MAP sensor that's drifted high, a vacuum leak large enough to push MAP toward atmospheric at idle, or a discrete BARO sensor reading low.
Cheapest-first ladder
- Scan live data at KOEO and compare MAP voltage to BARO voltage — they should both read 1.0-1.5V at sea level, lower at altitude (about 0.1V lower per 2,000 ft of elevation). If they disagree at KOEO, the higher-reading sensor is the suspect.
- Smoke-test the intake for vacuum leaks — a torn intake duct or blown intake-manifold gasket will push MAP up at idle because manifold vacuum is bleeding to atmosphere.
- Inspect the MAP vacuum port for carbon clog (high-mileage trucks) and the BARO sensor (if discrete) for moisture intrusion.
- Verify altitude programming if the truck was recently shipped from sea level to a high-elevation market — some early LS PCMs need a BARO relearn. Don't replace the BARO sensor before smoke-testing the intake — the most common P1108 cause on high-mileage LS trucks is a torn intake manifold gasket allowing manifold pressure to rise toward atmospheric, not a failed sensor.
Vehicle-specific patterns1999-2007 Silverado / Tahoe / Suburban / Yukon / Escalade with the LS-based 4.8/5.3/6.0 (LM7, LR4, LQ4, LY5) — the early LS intake manifold gaskets a…
- 1999-2007Silverado / Tahoe / Suburban / Yukon / Escalade with the LS-based 4.8/5.3/6.0 (LM7, LR4, LQ4, LY5) — the early LS intake manifold gaskets are a known leak point at the front and rear cylinder ports, and the leak shows up as P1108 paired with lean trims and P0171/P0174.
- 2005-2010Cobalt / G5 / HHR with the 2.2/2.4 Ecotec throws P1108 from a cracked plastic intake manifold (GM superseded the manifold under multiple PI bulletins).
- 2010+Camaro / CTS / Traverse with the LFX/LLT 3.6L V6 throws P1108 less commonly but when it does, it's usually carbon buildup at the MAP port distorting the reading.
- 2006-2010Silverado HD 6.6L LBZ/LMM Duramax uses a separate boost sensor and barometric pressure sensor — P1108 on the diesel typically points at a soot-fouled boost sensor reading high, not an intake leak.
Estimated repair$0 (relearn/recalibration after altitude change) to $650 (intake manifold gasket replacement on an LS truck).
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