VAG P1338 Fault Code: Camshaft Position Sensor (G40) Open Circuit / Short to B+
If your VW, Audi, SEAT or Skoda is throwing a P1338 fault code, it’s an electrical fault on the camshaft position sensor circuit on Bank 1 – specifically an open circuit or a short to battery voltage (B+). The verified VAG definition is “Camshaft Position Sensor (G40), Bank 1: Open Circuit or Short to Plus (B+)” (Ross-Tech 17746). P1338 is the mirror failure of P1337 (which is short-to-ground): same sensor, opposite electrical failure mode.
This guide explains what P1338 actually means on a VAG vehicle, the symptoms drivers notice, the realistic causes, and how a workshop properly diagnoses and repairs it. If you’d prefer a professional VAG-level diagnostic check at our Worthing workshop, we use VAG-specific scan software and oscilloscope test gear so the cam sensor circuit can be properly isolated.
What P1338 actually means on a VAG vehicle
P1338 is a VAG manufacturer-specific Diagnostic Trouble Code (its VAG-internal number is 17746). The “P1” prefix tells you it’s manufacturer-defined rather than a generic SAE J2012 code. On Volkswagen, Audi, SEAT and Skoda vehicles, P1338 is defined as “Camshaft Position Sensor (G40), Bank 1: Open Circuit or Short to Plus (B+)”.
The camshaft position sensor (component code G40 in VAG terminology) is a Hall-effect sensor mounted at the front of the engine. It detects the rotation of a reluctor wheel on the camshaft and sends a pulsing signal to the engine control unit. The ECU uses that signal alongside the crankshaft position sensor (G28) to know exactly where each piston is in its stroke, which determines ignition and injection timing.
P1338 is logged when the ECU sees the cam sensor signal either disappear completely (open circuit – a broken wire or failed sensor element) or jump to battery voltage (short to B+ – a damaged wire touching a 12V supply or a sensor failed to that condition). Either way, the expected pulsing signal is gone and the ECU can no longer trust the cam timing data. P1338 is an electrical-fault code on the sensor circuit – it doesn’t say anything about combustion, ignition coils or fuelling.
P1338 in the cam sensor code family
P1338 sits in a small family of VAG-specific cam sensor codes that describe different electrical failure modes of the same G40 sensor on Bank 1:
Working out which one you’ve got matters because the diagnostic approach differs slightly for each.
- P1337 – G40 cam sensor Bank 1: Short to Ground (signal stuck at 0V)
- P1338 – G40 cam sensor Bank 1: Open Circuit or Short to Plus (B+) – the opposite electrical failure
- P1340 – G40 cam sensor and G28 engine speed sensor: Incorrect Correlation (signals present but out of sync – often caused by timing-chain stretch on EA888 engines)
Common symptoms of P1338
Engine management light
The MIL is the most reliable sign. P1338 is normally a hard-fault code that stays on once the sensor or wiring has failed – though intermittent broken cores in the loom can produce a code that comes and goes.
Long cranking or no-start
Without a usable cam signal the ECU has to fall back on the crankshaft sensor alone to synchronise ignition and fuelling. On many VAG engines this means longer-than-normal cranking before the engine fires, and on some it means the engine won’t start at all. Hot starts can be particularly affected.
Rough idle and hesitation
When the engine does run, the lack of accurate cam timing data tends to produce a rough or hunting idle and hesitation when accelerating. The car may feel flat under load and unresponsive to throttle inputs.
Limp mode
Some VAG engines drop into limp mode when P1338 is active to protect the engine from running on poor timing data. Power is reduced and revs are typically capped around 3,000 rpm.
Worse fuel economy
Running on default ignition and fuelling maps usually costs noticeable mpg.
What causes P1338 on VAG vehicles
1. Failed G40 cam position sensor
The most common cause is the sensor itself failing internally in an open-circuit condition. G40 sensors are wear items and tend to fail at higher mileage or after long-term heat exposure. On Audi A4/A6 B6-B7 and VW Passat B5/B6, the G40 is a well-documented weak point and often presents as intermittent hot-start problems before failing outright.
2. Broken signal wire in the loom
The G40 wiring runs across the top of the engine and is exposed to heat, vibration and the occasional touch from a service job. A broken core inside the signal wire (often where the loom flexes near the valve cover) produces the same open-circuit symptom as a failed sensor. Broken cores can be intermittent at first and only show up as P1338 when the engine warms up and the wire expands enough to lose contact.
3. Connector contamination or damage
Oil contamination inside the G40 connector – usually from a leaking valve cover or rocker cover gasket – is a classic VAG failure point. The connector pins can also corrode, become pushed back during a previous service, or develop poor contact. Any of these can produce an open-circuit reading at the ECU.
4. Short between signal wire and a 12V supply
Less common than the open-circuit failure modes but still possible: a chafed harness touching a power feed somewhere in the engine bay produces the “short to B+” failure mode the code description references.
5. ECU internal fault (rare)
A failure in the ECU’s input circuit for the cam sensor can also produce P1338, but this is very rare and should only be diagnosed after the sensor and wiring have been confirmed good.
Diagnostic process for P1338
Step 1 – VAG-level scan
A dealer-level scan tool (VCDS, ODIS or equivalent) reads the exact P1338 wording and the freeze-frame data: engine load, speed, coolant temperature and battery voltage at the moment the fault was logged. This often points the diagnosis. If P1337 is also present, suspect a shared wiring or connector issue affecting both failure modes.
Step 2 – Inspect the G40 connector and loom
The G40 connector is unplugged and inspected for oil contamination (a tell-tale sign of a leaking valve cover gasket), corroded pins, pushed-back terminals and heat damage. The wiring back along the loom is traced for broken cores, chafed insulation, and any places where the harness may have touched a 12V feed.
Step 3 – Multimeter checks
With the wiring diagram on hand and the connector unplugged, the technician checks the 5V supply at the connector (key on, engine off), the ground continuity, and signal-wire continuity from the connector back to the ECU. Any break in the signal wire confirms an open circuit; voltage where there should be none confirms a short to B+.
Step 4 – Live data + oscilloscope where needed
With everything reconnected and the engine cranking, live cam sensor data shows whether the sensor is producing any output at all. For intermittent faults that don’t show statically, an oscilloscope on the signal wire reveals the pulse pattern (or absence of it) and isolates whether the fault is at the sensor or in the wiring.
Step 5 – Sensor substitution
If wiring and connector are confirmed good and the live data still shows no usable signal, the sensor itself is replaced with an OE-spec or recognised aftermarket equivalent (typical brands: Bosch, VDO/Continental). Generic universal sensors are not recommended for VAG cam timing applications.
Repair solutions
G40 sensor replacement
If the diagnosis confirmed a failed sensor, replacement is normally straightforward on most VAG engines. Always use OE-spec or recognised aftermarket parts – the cam timing function is critical and cheap aftermarket sensors are a known cause of repeat faults.
Wiring or connector repair
If wiring or connector damage is at fault, the correct repair is to splice in a new section of correctly-rated wire, fit a new connector body if the pins are damaged, and protect the harness with proper sheathing. Heat-shrink tubing and loom tape used together is the standard.
Address the root cause if oil contamination is found
If the connector was full of oil, the underlying cause is a failing valve cover or rocker cover gasket. Replacing the gasket properly stops oil migrating back into the new connector and prevents the next sensor from failing prematurely. Particularly common on the 1.4 TSI and 2.0 TFSI EA888.
Clear the code and verify
Once fixed, the code is cleared and the car is driven through a full drive cycle so the OBD readiness monitors complete. The technician confirms P1338 doesn’t return, no related cam/crank codes log, and the engine cranks and idles cleanly.
Is it safe to drive with a P1338 code?
Short trips are usually possible, but the car may refuse to restart hot, may stall unexpectedly, or may run in limp mode. Stalling at junctions or on faster roads is a genuine safety risk, so it’s not a fault to leave for any length of time. If the engine is hot-stalling or has refused to start at any point, book a diagnostic check before relying on the car for longer journeys – our Worthing diagnostics team can identify whether it’s the sensor, wiring or connector in a single visit.
Will P1338 fail the MOT?
Yes. Under current DVSA MOT rules an engine management light that stays on with the engine running is an automatic fail under the malfunction indicator lamp check. A no-start or stalling caused by P1338 will also stop the tester completing the emissions portion of the test. Repair the cam sensor or wiring fault, clear the code, complete a short drive so the OBD readiness monitors set, then present the car for MOT.
VAG models most affected by P1338
P1338 appears across the VAG range, particularly on Audi A3/A4/A6, VW Golf, Passat and Polo, SEAT Leon and Skoda Octavia fitted with the 1.8T, 2.0 TFSI EA888, 1.4 TSI, and older 1.6 and 2.0 FSI engines. The G40 sensor is a well-known wear item on these platforms and the loom running close to engine bay heat is a frequent failure point. Our Volkswagen specialist team and Audi specialist team diagnose the G40 sensor family routinely.
Conclusion
P1338 on a VAG vehicle is the G40 camshaft position sensor on Bank 1 reporting an open-circuit or short-to-B+ electrical fault – the mirror of P1337 (short-to-ground). The dominant causes are a failed sensor, broken signal wire in the loom, and connector damage from oil contamination. Proper diagnosis takes about 30 minutes with VAG-level scan software and a multimeter and rules out most causes before any parts are bought.
If you’re local to West Sussex, you can book a VAG diagnostic check with our Worthing team and we’ll identify whether it’s the sensor, the loom or the connector in one visit. For a wider explanation of how VAG fault codes are structured, see our complete VAG error-code reference.
Frequently Asked Questions about P1338
P1338 is a VAG manufacturer-specific code (VAG number 17746). On Volkswagen, Audi, SEAT and Skoda vehicles it is defined as ‘Camshaft Position Sensor (G40), Bank 1: Open Circuit or Short to Plus (B+)’. The ECU has detected that the cam sensor’s signal circuit is either broken (open circuit) or shorted to battery voltage – the opposite electrical failure mode to P1337 (which is short-to-ground).
Related fault codes
Other codes affecting the same system. A stored code often arrives alongside its neighbours.
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