P0370 – Timing reference, high resolution signal A -malfunction

By Reinier (Contact Me)
Last Updated 2017-08-12
Automobile Repair Shop Owner

Table of Contents

1. What Does Code P0370 Mean?
2. What are the common causes of code P0370 ?
3. What are the symptoms of code P0370 ?
4. How do you troubleshoot code P0370 ?
5. Codes Related to P0370
6. Get Help with P0370

What Does Code P0370 Mean?

OBD II fault code P0370 is a generic code that is defined as “Timing reference, high resolution signal A – malfunction”, and is set when the PCM (Powertrain Control Module) fails to detect a timing reference signal. Note that while this code primarily refers to a problem in an engine position sensor (aka crankshaft position sensor) circuit, failure of engine position sensors can also cause this code to set.

In order for the PCM on any modern application to control and monitor engine speed, fuel injection strategies, ignition timing, (fuel injection timing on diesels), and misfire diagnostics effectively, it requires a timing reference signal that tells the PCM where the crankshaft (and hence the #1 piston) is during a crankshaft rotation. In other words, the PCM needs to know how many degrees of rotation the crankshaft has completed during a rotation, relative to a fixed starting point.  In a fully functional system, the generated signal is delivered to the PCM via a dedicated signal circuit, or a varying resistance in the case of two-wire sensors.

In practice, this timing reference signal is generated by a sensor whose magnetic field is interrupted by the teeth on a reluctor wheel that (depending on the application) can be located on the crankshaft pulley (aka harmonic balancer), a camshaft,  flywheel or flex plate, or inside the fuel pump on some diesel applications. Refer to the Trouble Shooting section of this guide for more details on the types of engine position sensors in use today.

The image below shows the typical arrangement of an engine position sensor and its reluctor ring, which in this case, is located on the harmonic balancer. Note that while this particular example is adjustable by means of the slotted mounting slots, most engine position sensors are not adjustable.

What are the common causes of code P0370 ?

Some common causes of code P0370 could include the following-

• Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
• Defective engine position sensor
• Defective or clogged reluctor ring
• Failed or failing PCM. Note that this is a rare event, and the fault must be sought elsewhere before any control module is replaced

What are the symptoms of code P0370 ?

Some common symptoms of code P0370 could include the following-

• Stored trouble code and an illuminated warning light
• Poor engine performance
• Some applications may exhibit severe misfires
• In some cases, a hard or no start condition may be present
• If the engine starts and runs, fuel consumption may increase dramatically

How do you troubleshoot code P0370 ?

NOTE #1: Note that the reluctor is not always visible r easily accessible. However, in cases where the reluctor ring is accessible, inspect the ring for obvious signs of damage and/or evidence of foreign material such as mud that may be clogging the gaps between teeth as a first step.  If teeth are damaged / broken, or if the ring is fractured, the only reliable remedy is replacement of the ring. If however the gaps on the reluctor ring are merely clogged, removal of the foreign matter will resolve the code, provided that the sensor itself is not damaged.

NOTE #2: Depending on the application, the engine position sensor can have either two, or three wires, which means that testing procedures vary. Below are some details of each type of sensor-

– Hall Effect Sensors: 

These sensors have three wires; one wiring being a ground, one wire being a reference voltage input, and the other being a dedicated signal wire to carry the generated signal back to the PCM. The (usually) 5-volt reference voltage is required to energize the electromagnet that generates the signal when the magnetic field is interrupted by the teeth on the reluctor ring.

– Permanent Magnet Sensors:

These sensors have only two wires, one being a ground, and the other being the signal wire that carries the generated signal back to the PCM.  As the name suggests, the magnets in these sensors are of the permanent type, and therefore these sensors do not require a reference voltage. As with Hall Effect sensors, the teeth on the reluctor ring interrupt the magnetic field, which generates the timing signal.

Step 1

Record all fault codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on.

Step 2

Refer to the manual to locate and identify the engine position sensor. Also determine the function and color-coding of each wire in the sensor, and perform a thorough visual inspection of the entire wiring harness, all the way to the PCM connector. Look for damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors. Make repairs or replace wiring as required.

Step 3

If no visible damage is found, prepare to perform reference voltage (where applicable), resistance, continuity, and ground integrity tests on all associated wiring, but be sure to disconnect the wiring from both the sensor and the PCM to prevent damage to the controller, and to ensure the most accurate test results.

NOTE #1: In the case of Hall Effect sensors, pay particular attention to the resistance of the signal wire, since an abnormally high resistance can influence the operation of the sensor. Make repairs or replace wiring as required to ensure that the resistance of the signal circuit conforms to specified values.

NOTE #2: If there is no voltage in the reference voltage circuit, or if the reference voltage is significantly lower than 5 volts, be sure to check (at the PCM connector) that the PCM actually delivers the correct voltage. If it does not, replace the PCM.

NOTE #3: In the case of permanent magnet sensors, pay particular attention to the ground circuit. In most cases the ground is supplied by the PCM, so make sure that all terminals/pins in all connectors are corrosion free and in perfect condition. Replace connectors that are in a less than perfect condition.

Step 4

If all electrical values in the circuit check out, disconnect the sensor from its wiring and connect the black lead of the multimeter to the ground, and the red lead to the signal wire, regardless of the type of sensor. Have an assistant crank the engine in short bursts; if the sensor works, the multimeter will display a voltage that will vary between 0 and 5 volts (or very close to 5 volts) as the engine rotates.

If no voltage is shown on the multimeter, the sensor is defective and must be replaced, but be sure to only replace engine position sensors with OEM replacements to ensure proper operation of the engine management system.

Step 5

If the fault persists but the sensor is known to be in working order and the wiring checks out, it may be necessary to have the fault diagnosed with advanced diagnostic equipment that could include an oscilloscope. If such equipment and reference data is not available, the better option is to refer the vehicle to the dealer or other competent repair facility for professional diagnosis and repair, since the diagnosis may involve partial disassembly of the engine and/or transmission to inspect/replace the reluctor ring.

Codes Related to P0370

• P0371 – “Timing Reference High Resolution Signal A Too Many Pulses”
• P0372 – “Timing Reference High Resolution Signal A Too Few Pulses”
• P0373 – “Timing Reference High Resolution Signal A Intermittent/Erratic Pulses”
• P0374 – “Timing Reference High Resolution Signal A No Pulses”

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