| Camshaft Position Sensor “A” Circuit Malfunction
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|Wiring, CMP sensor, ECM
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Table of Contents
- What Does Code P0340 Mean?
- Where is the P0340 sensor located?
- What are the common causes of code P0340?
- What are the symptoms of code P0340?
- Get Help with P0340
What Does Code P0340 Mean?
Special note on trouble code P0340 and Toyota vehicles: While DTC P0340 is a generic code that affects all OBD II compliant vehicles, the most common causes of this code sometimes vary between most vehicle makes. This article will therefore deal with code P0340 as it applies specifically to Toyota vehicles.
OBD II fault code P0340 is a generic trouble code that is defined as “Camshaft position (CMP) sensor A – Bank 1 – circuit malfunction” and is set when the PCM (Powertrain Control Module) detects a failure, defect, or malfunction in the control, signal, or reference voltage circuit(s) of the position sensor that is associated with the intake camshaft on Bank 1. Note that “Bank 1” refers to the bank of cylinders on V-type engines that contains cylinder #1.
While several details of the ignition systems on Toyota vehicles differ somewhat from the ignition systems of most other vehicle brands, Toyota ignition systems are not so radically different from other systems that they are problematic, or difficult to diagnose.
However, for a Toyota engine to start, it needs input data from and the camshaft position sensor to not only determine the position of piston #1 relative to the position of the engine valves in cylinder #1, but also to control the ignition timing, injection timing, and VVT (Variable Valve Timing) systems during the engine start-up process.
What the PCM is looking for before engine start-up is verification that piston #1 is near the top of its compression stroke and that the intake valve(s) on cylinder #1 is about to close. In practice, the PCM uses this information to calculate the appropriate moment to a) deliver the ignition spark and b), to open injector #1 to inject fuel into cylinder #1. Therefore, to do this correctly and consistently, the positions of the crankshaft and camshaft must correlate exactly to a) ensure peak engine performance, and b) to reduce exhaust emissions by ensuring proper combustion of the air/fuel mixture.
We need not delve into the technical details of each type of camshaft position sensor in current use here, beyond saying that Toyota vehicles are typically fitted with magnetic-type sensors, which create electrical signals when a rotating reluctor ring or protrusion on the camshaft passes in front of the sensing element. In terms of operation, the camshaft position sensor is supplied with a 5-volt reference voltage that switches between “ON” and “OFF” states as the camshaft rotates.
Thus, by monitoring the state of the signal, the PCM can correlate the crankshaft’s position with that of the camshaft as a means to verify that the engine’s valve, ignition, and injection timing are all within a specified range before starting the engine. Therefore, if the position of the intake camshaft does not correlate with any other timing aspect because the PCM does not receive an input from the camshaft position sensor, or the PCM receives an implausible signal from the sensor, the PCM will recognize that it cannot control the fuel delivery and ignition systems effectively.
When this happens, the PCM on most Toyota applications will set code P0340 within a predetermined time after an engine start-up attempt or within 10 seconds after the engine has started, which brings us to-
What causes code P0340 on Toyota vehicles?
As with most other generic trouble codes, there is neither a single cause of code P0340 nor a unique set of circumstances that will cause this code to set more often on Toyota vehicles than on any other brand of vehicle.
However, there is one exception to this general rule. On most Toyota applications, the battery voltage plays a critical role during engine cranking, and this voltage serves as one of the principal enabling conditions that will set a host of fault codes. In the case of code P0340, a battery voltage of 11 volts or less will be the principal reason why the code sets, even though the camshaft position sensors and its associated circuits may be in perfect working order. Therefore, checking and verifying the battery voltage during engine cranking should always be the first step in any diagnostic procedure in cases where code P0340 is present.
Note though that when a defective camshaft position sensor is suspected, the wisest course of action would be to replace it with an OEM part to ensure reliable operation of the sensor. See the section on Common Causes for more details on other possible causes of code P0340 on Toyota vehicles.
Where is the P0340 sensor located?
This image shows the location (circled) of the camshaft position sensors on a 2014 to 2018 Toyota Highlander SUV fitted with the 2GR-FKS 3.5L V6 engine. Note though that while the sensors are relatively easy to access on this application, it may be necessary to remove or disassemble some engine components to gain easy access to the camshaft position sensors on many other Toyota applications.
Therefore, be sure to consult reliable service information for the affected vehicle to locate and identify the camshaft position sensor(s) correctly.
What are the common causes of code P0340?
The most common causes of code P0340 on Toyota vehicles are largely similar across all Toyota applications, and could include one or more of the following, but note that possible causes are listed here in their order of prevalence, with the most prevalent causes listed first-
- Burnt, damaged, shorted, disconnected, or corroded wiring in the sensors’ reference and/or signal circuits
- Failed or failing camshaft position sensor, or the use of an unsuitable aftermarket sensor
- Failures, defects, or malfunctions in the variable valve or camshaft systems that prevent the camshaft from returning to its base position after engine shutdown. Note that this is more likely to be caused by low oil pressure and/or old, dirty, or degraded engine oil causing variable valve timing components to bind or stick than by actual failures of variable valve timing system components
- Damaged or worn valve timing components such as worn timing belts/chains, worn or damaged timing chain guides, or worn timing sprockets
- Failed or failing crankshaft position sensor, but note that this will usually be indicated by one or more dedicated crankshaft position sensor trouble codes
- Failed or failing PCM, but note that since this a rare event, the fault must be sought elsewhere before any control module is reprogrammed or replaced
What are the symptoms of code P0340?
Common symptoms of code P0340 on Toyota vehicles are largely similar across all Toyota vehicles and could include one or more of the following. Note, however, that depending on the vehicle and the nature of the problem, the severity of one or more symptoms listed here can vary substantially between applications-
- Stored trouble code and illuminated warning light
- Depending on the nature of the problem, multiple additional codes may be present along with P0340
- The engine may start, but shuts off again almost immediately
- The engine may only start after extended periods of cranking
- If the engine starts and runs, the idling quality may be poor, and persistent misfires may be present
- Varying degrees of power loss may be present- if the engine starts and runs at all
- The engine may stall repeatedly and/or unexpectedly at low engine speeds
- Fuel consumption may increase noticeably
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