OBD-II Code
P1240
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)
$40–$400
From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
$40 (single shorted sensor replacement + harness inspection DIY) to $400 (multiple sensor replacement + ECM ground-point refresh + harness repair at a Saab specialist).
P1240 on a Saab is Sensor Power Supply Voltage Low — the ECM's internal 5V VREF supply that powers TPS, MAP, MAF, and other analog sensors has dropped below the healthy 4.9-5.1V window, typically to 4.5V or lower.
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 procedureP1240 on a Saab is Sensor Power Supply Voltage Low — the ECM's internal 5V VREF supply that powers TPS, MAP, MAF, and other analog sensors has droppe…
P1240 on a Saab is Sensor Power Supply Voltage Low — the ECM's internal 5V VREF supply that powers TPS, MAP, MAF, and other analog sensors has dropped below the healthy 4.9-5.1V window, typically to 4.5V or lower. A failing 5V VREF rail upstream poisons every analog sensor downstream simultaneously, which means P1240 often shows up alongside seemingly random sensor-range codes (TPS, MAP, IAT) and chasing those individual codes is a waste of time until the VREF supply itself is fixed.
Cheapest-first ladder
- Backprobe the 5V reference at any convenient sensor connector with the key on and engine off — TPS or MAP are easiest — and confirm the actual voltage. Healthy is 4.9-5.1V; anything below 4.8V is the real problem regardless of what other codes are also present.
- If VREF is low at one sensor, check it at another sensor on a different harness branch — if VREF is low everywhere, the supply itself (inside the ECM) is failing or is being pulled down by a shorted sensor; if VREF is low at one branch only, suspect a chafed harness shorting VREF to ground partway down that branch.
- Disconnect sensors one at a time while monitoring VREF — if disconnecting a specific sensor restores VREF to 5.0V, that sensor's internal resistance has collapsed and is pulling the rail down.
- Check ECM B+ and ground points before condemning the ECM — Saab ECMs are sensitive to ground-point corrosion at the chassis stud near the strut tower on 9-3 cars and behind the battery tray on 9-5 cars. Do NOT throw a $700 ECM at P1240 without disconnecting sensors one at a time to find the downstream short — a single shorted MAP or TPS pulling 5V to ground will mimic a failed ECM rail and the ECM itself is almost never the actual problem.
Vehicle-specific patterns1997-2010 Saab 9-5 with the B205/B235 2.3L turbo is the most common P1240 platform — the MAP sensor in the intake manifold and the boost-pressure sen…
- 1997-2010Saab 9-5 with the B205/B235 2.3L turbo is the most common P1240 platform — the MAP sensor in the intake manifold and the boost-pressure sensor downstream of the intercooler both have a known internal-short failure mode at 100K+ mi that pulls 5V VREF down.
- 2003-2011Saab 9-3 with the B207 2.0L turbo throws P1240 from MAP sensor failure and from harness chafe at the engine-cover anchor points where the wiring rubs the cover edge.
- 1999-2003Saab 9-3 (first generation) with the B205 throws P1240 from the same MAP/TPS pattern as later cars.
- 2005-2009Saab 9-7X (5.3L Vortec V8) inherits GM code definitions and does not throw Saab-specific P1240.
Estimated repair$40 (single shorted sensor replacement + harness inspection DIY) to $400 (multiple sensor replacement + ECM ground-point refresh + harness repair at a Saab specialist).
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