P1337 VAG Fault Code: Camshaft Position Sensor (G40) Short to Ground

P1337 in the cam sensor code family

P1337 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)

Engine management light

The MIL is the most reliable sign. P1337 is normally a hard-fault code that stays on once the sensor or wiring has failed.

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 P1337 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.

1. Failed G40 cam position sensor

The most common cause is the sensor itself failing internally in a way that pulls its output to ground. 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. Wiring damage between the sensor and ECU

The G40 wiring runs across the top of the engine and can chafe against metal edges, get damaged during other service work, or have its insulation degraded by heat. A signal wire chafed through to a grounded surface produces an electrical short that the ECU sees as a permanent low reading.

3. Connector contamination or damage

Oil contamination inside the G40 connector – usually from a leaking valve cover or rocker cover gasket – is a common VAG failure point. The connector pins can also corrode, become pushed back during a previous service, or develop poor contact, all of which can produce shorted or unstable signals.

4. Lost 5V supply to the sensor

G40 is a Hall-effect sensor and requires a 5V reference from the ECU to work. If the supply line is broken, the sensor’s output collapses to 0V and looks identical to a short-to-ground from the ECU’s perspective. A genuine ECU 5V supply failure is rare and usually shows up alongside faults on other sensors that share the same supply.

5. ECU internal fault (rare)

A failure in the ECU’s input circuit for the cam sensor can also produce P1337, but this is very rare and should only be diagnosed after the sensor and wiring have been confirmed good.

Step 1 – VAG-level scan

A dealer-level scan tool (VCDS, ODIS or equivalent) reads the exact P1337 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. Common paired codes include P1340 (cam/crank correlation), which can suggest timing-chain wear on EA888 engines, and P0341 (cam sensor range/performance).

Step 2 – Visual inspection of 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 chafed insulation, particularly where it crosses metal edges or runs near the exhaust manifold.

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 the signal-wire continuity from the connector all the way back to the ECU. A short between the signal wire and a grounded surface anywhere along the loom will register as continuity where there should be none.

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 test

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.

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 P1337 doesn’t return, no related cam/crank codes log, and the engine cranks and idles cleanly.