OBD-II Code
P1233
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)
$80–$1,400
From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
$80 (corroded relay/connector clean-up) to $1,400 (full in-tank pump module plus EKP control module replacement on a W221 S550).
P1233 on a Mercedes is a Fuel Pump Stage 1 circuit fault — Mercedes runs a two-stage fuel pump strategy on the M271/M272/M273 platforms (some via in-tank pump module, some via PWM-controlled relay/EKP module), and stage 1 is the low-pressure circuit that primes the rail at idle and light throttle.
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 procedureP1233 on a Mercedes is a Fuel Pump Stage 1 circuit fault — Mercedes runs a two-stage fuel pump strategy on the M271/M272/M273 platforms (some via in-…
P1233 on a Mercedes is a Fuel Pump Stage 1 circuit fault — Mercedes runs a two-stage fuel pump strategy on the M271/M272/M273 platforms (some via in-tank pump module, some via PWM-controlled relay/EKP module), and stage 1 is the low-pressure circuit that primes the rail at idle and light throttle. The ECU watches commanded duty cycle versus measured current draw on the stage 1 circuit; when commanded duty sits at 30-60% at idle but current draw drops below ~3A (typical healthy stage 1 pulls 5-8A at idle, 8-12A under load, and a healthy stage 2 add-on brings total system draw to 10-15A at WOT), it sets P1233.
Diagnostic order on the shop floor
- Scan live data with XENTRY or a capable bidirectional scanner — look at "Fuel Pump Stage 1 Commanded Duty" (0-100%) and "Fuel Pump Stage 1 Current Draw" (Amps). If duty is pegged at 80-100% and current is below 2A, the pump or its wiring is the problem; if duty matches expected (30-50% at idle) and current is normal but the code still sets, the EKP control module itself is failing.
- Check the fuel pump relay/EKP module under the rear seat or in the trunk — corrosion on the connector is shockingly common on W211/W221 cars and clears the code for $0.
- Drop the rear seat and ohm the pump motor (healthy is 0.5-2 ohms across the motor terminals; open-circuit means the brushes have worn out). Expensive-misdiagnosis caveat: don't replace the in-tank pump assembly before verifying the EKP control module is actually commanding the pump — the EKP module on W211/W221 cars fails internally and reports phantom low-current faults, and dropping a brand-new $400 pump into a tank only to find the $300 EKP module was the real culprit is a Saturday-morning special at every Mercedes independent shop.
Vehicle-specific patterns2005-2011 Mercedes C-Class/E-Class/S-Class with the M272 3.0L/3.5L V6 or M273 4.6L/5.5L V8 (W203/W204/W211/W212/W221) throws P1233 most often from a…
- 2005-2011Mercedes C-Class/E-Class/S-Class with the M272 3.0L/3.5L V6 or M273 4.6L/5.5L V8 (W203/W204/W211/W212/W221) throws P1233 most often from a corroded EKP relay connector or from the in-tank pump module wearing out around 100-130K miles — the cars also famously suffer balance-shaft gear wear that's covered by an extended warranty on affected VINs, but that's a P0016/P0017 issue not a fuel pump issue.
- 2003-2014Mercedes C-Class/SLK with the M271 1.8L Kompressor (C230/C250/SLK200) throws P1233 from the same EKP corrosion pattern plus a known intake-manifold tumble-flap failure that loads the pump harder than spec.
- 2007-2010Mercedes E320/E350 BlueTec and ML320 BlueTec with the M642 3.0 diesel use a different high-pressure pump architecture, but the low-pressure lift pump still sets P1233 when its wiring corrodes at the tank-top bulkhead connector.
- 2007-2014Sprinter vans with the OM642 are notorious for fuel-pump-circuit codes from chassis-flex fatigue at the wiring loom.
Estimated repair$80 (corroded relay/connector clean-up) to $1,400 (full in-tank pump module plus EKP control module replacement on a W221 S550).
Look up another code
More free tools