P0335 on a Duramax LMM: Crankshaft Position Sensor and What Actually Causes It
TL;DR: P0335 is a crankshaft position sensor circuit fault. It tells you the engine control module lost or never saw a usable crank signal, not that the sensor has failed. On a 2007.5 through 2010 6.6L Duramax LMM the same code comes from chafed wiring, a corroded connector, a damaged reluctor wheel or a charging and grounding problem just as often as it comes from a bad sensor. Test the circuit before you buy the part, and plan on the crankshaft position variation learn procedure afterward.
What P0335 actually means
The crankshaft position sensor is how the engine control module knows where the crankshaft is and how fast it is turning. It reads a toothed reluctor wheel that turns with the crankshaft, and the gaps in that tooth pattern give the module a reference point it can sync to. Without that signal the module cannot decide when to command an injection event, so on a diesel a total loss of crank signal is a no-start, not a rough runner.
P0335 is the generic OBD-II definition for a crankshaft position sensor "A" circuit fault. It is set when the module either sees no signal at all while the engine is turning, or sees a signal so electrically wrong that it cannot be used. That is a deliberately broad definition, and it is why the code alone does not name the failed component. Everything between the reluctor teeth and the module's input pin is inside the accusation: the wheel, the air gap, the sensor, the connector, the harness, the shield and ground, the supply voltage, and the module input itself.
Related codes narrow it considerably, so pull all of them before deciding anything:
- P0336 is a crank sensor range or performance fault. The module is getting a signal, but the pattern is wrong. That points harder at the reluctor wheel, the air gap or an intermittent connection than at an open circuit.
- P0340 or P0341 are camshaft position sensor codes. A crank code sitting next to a cam code changes the conversation toward shared power and ground, harness routing, or a timing problem.
- P0016 and its relatives are crank and cam correlation codes. Two sensors that each work but disagree about where the engine is means you look at timing gear condition and reluctor damage, not at a sensor.
- Charging or system voltage codes alongside P0335 are a strong hint that the real fault is electrical supply, not the sensor.
Read the freeze frame while you are in there. A P0335 that set at cranking speed on a cold morning is a different fault from one that set at road load and full operating temperature, and the freeze frame costs nothing.
The LMM specifics that change the diagnosis
The LMM is the 2007.5 through 2010 6.6L Duramax. A handful of things about it matter for this code, and generic advice written for a gasoline V8 will send you the wrong way.
There is no ignition system to blame. The LMM is a compression-ignition diesel. It has no spark plugs, no coils, no plug wires and no knock sensor. If a suggested cause list for your crank sensor code mentions any of those, it was not written for this engine. What it does have is glow plugs for cold starting, and they have nothing to do with P0335.
It is a pushrod V8. Camshaft in the block, hydraulic lifters, pushrods. There are no lash adjusters or cam followers to inspect here, and the crank and cam timing relationship is set by the gear drive at the front of the engine. That matters when you get correlation codes alongside the crank code.
The high-pressure pump is a CP3. The LMM uses the Bosch CP3, which is the pump generation before the CP4 that arrived on the later LML. That is worth knowing because a lot of Duramax troubleshooting written online is CP4 contamination advice, and it does not transfer to this truck. It also means a no-start on an LMM is far more likely to be a signal or supply problem than a pump failure.
Access drives the labour, not the part cost. The sensor reads a reluctor wheel on the crankshaft from a mount low on the engine, and getting to it is most of the job. Confirm the exact location and removal sequence for your model year in the service manual before you quote the work.
A relearn is part of the repair. GM calls for a crankshaft position variation learn procedure with a capable scan tool after crank sensor and related repairs on these engines. Skipping it can leave you with a truck that runs but sets codes again. Budget the scan tool time into the job and follow the service manual procedure for your year.
The causes, in the order worth testing
Cheapest, most reversible and most likely first. This is roughly how a diesel tech works an LMM with P0335 and no other useful codes.
| Suspect | What points to it | How to confirm | Typical shop labour |
|---|---|---|---|
| Corroded or backed-out connector pin | Intermittent stall, code clears and returns, wiggle-sensitive | Inspect and load-test the connector, check pin tension and terminal corrosion | Light |
| Chafed or rubbed-through harness | Fault appears with vibration, road speed or engine movement | Follow the harness routing, inspect at every clip and pass-through | Light to moderate |
| Poor ground or shield integrity | Crank code alongside cam or charging codes, noisy live data | Voltage drop test the grounds, verify shield continuity per the wiring diagram | Light to moderate |
| Low system voltage or weak batteries | No-start with slow cranking, multiple unrelated codes at once | Load test both batteries and the charging system before anything else | Light |
| Failed crankshaft position sensor | Consistent no-start or hot-soak stall, no signal on the scope while cranking | Scope or scan-tool signal check while cranking, compare against the service manual waveform | Moderate, access driven |
| Damaged, loose or contaminated reluctor wheel | Range or performance codes, correlation codes, signal present but wrong | Inspect the wheel and air gap, look for debris and impact damage | Heavy |
| Timing gear wear or a timing problem | Crank and cam correlation codes together, hard starting, noise | Verify gear condition and timing per the service manual before condemning sensors | Heavy |
| Module input or connector fault | Everything upstream tests good, signal present at the module but not seen | Diagnose per the factory pinpoint test; last resort, not first guess | Heavy |
Two rules keep this cheap. First, scope the sensor circuit while the engine is cranking rather than guessing from a static resistance reading, because a sensor that measures fine sitting still can still drop out under heat and vibration. Second, if the fault is intermittent, wiggle-test the harness and connector with the circuit live before you order anything. Intermittent crank codes on trucks that work for a living are wiring far more often than hardware.
What to actually buy, and when
Work in this order and you will spend the least money.
- Nothing, until the circuit is tested. The sensor is the cheapest part in the repair and the most commonly replaced without cause. Test first.
- Connectors, terminals and harness repair. A pigtail, correct terminals and proper heat-shrink splices fix a large share of these. Harness and module-side parts are in harnesses and PCM/ECM.
- Batteries and charging, if voltage is marginal. Two weak batteries on a diesel produce a shopping list of codes that all disappear when the voltage is right.
- The sensor, once the data supports it. Confirm the current part number against the manufacturer catalogue for your exact year and configuration before ordering from engine sensors. Everything else LMM-specific lives under Duramax LMM parts.
- Reluctor and timing work last. If the wheel is damaged or the gear drive is worn, you are into a much larger job. Timing parts sit in timing chains, gears and tensioners, and the wider family catalogue is under Duramax 6.6 parts.
Torque the sensor fastener and every bracket you disturb to the value and sequence in the service manual for your exact year. Over-tightening a sensor into its housing is an easy way to turn a light job into a heavy one, and an incorrectly seated sensor changes the air gap that the whole signal depends on.
Frequently Asked Questions
Will a Duramax LMM start with a failed crankshaft position sensor? Usually not. The engine control module needs a crank reference to time injection, so a complete loss of signal is generally a crank-but-no-start. A truck that starts and stalls, or starts hot but not cold, is more often an intermittent circuit or connector than a dead sensor.
Can bad spark plugs cause P0335 on an LMM? No. The LMM is a diesel and has no spark plugs, coils or plug wires. It has glow plugs, and those assist cold starting only. Any advice sending you toward ignition parts on this engine was written for a gasoline engine.
Do I need a relearn after replacing the crankshaft position sensor? Plan on it. GM specifies a crankshaft position variation learn procedure with a scan tool after this kind of repair on these engines. Follow the procedure in the service manual for your model year rather than assuming the truck will sort itself out.
What is the difference between P0335 and P0336? P0335 is a circuit fault, meaning no usable signal reached the module. P0336 is a range or performance fault, meaning a signal arrived but the pattern was wrong. P0336 points harder at the reluctor wheel, the air gap or an intermittent connection.
Could this be the camshaft position sensor instead? It can be a shared cause. If you have crank and cam codes together, look at what the two circuits share before replacing either sensor: power feed, ground, shield and harness routing. Correlation codes specifically point at timing and reluctor condition rather than at a sensor.
Is it worth replacing the sensor as preventive maintenance? Not on its own. It is not a wear item with a published interval, and the access labour on this engine makes speculative replacement expensive. If the engine is already apart for other work in the same area, replacing it while you are in there is a reasonable call.
Sources
Written from the Core Powertrain Parts technical reference notes for the 2007.5 through 2010 6.6L Duramax LMM, the generic OBD-II definitions for crankshaft and camshaft position sensor codes, and the category structure of the Core Powertrain Parts catalogue. Torque values, resistance and air gap specifications, waveform references, pinpoint test steps and part numbers are deliberately not quoted here because they vary by model year and configuration. Confirm each against the factory service manual and the current manufacturer catalogue for your exact truck.
Questions on fitment for a specific year and cab configuration, contact sales@coretransmissionparts.com. Orders over $70 ship free.