AutoCodes – Generic – P0374

P0374 Code - Timing Reference High Resolution Signal 'A' No Pulses

Quick Answer

The optical sensor provides a high resolution signal to the Powertrain Control Module (PCM) by counting pulses on the sensor disk located in the injection pump. Common causes include Timing Reference Optical Sensor harness is open or shorted, Timing Reference Optical Sensor circuit poor electrical connection, Faulty Timing Reference Optical Sensor. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P0374 indicates Timing Reference High Resolution Signal 'A' No Pulses.
Common causes: Common causes include Timing Reference Optical Sensor harness is open or shorted, Timing Reference Optical Sensor circuit poor electrical connection, Faulty Timing Reference Optical Sensor.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 17,435

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jun 14, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
Comments
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Code P0374 Description

The optical sensor provides a high resolution signal to the Powertrain Control Module (PCM) by counting pulses on the sensor disk located in the injection pump. The high resolution is one of the most important inputs by the PCM for fuel control and timing. This test monitors the number of high resolution pulses which have been missed (not detected). It's based on a comparison between the number of pulses that were detected since the last pump cam pulse and the number of the pulses that should have occurred. There are approximately 64 high resolution pulses for every cam pulse.

OBDII Code P0374 - Timing Reference High Resolution Signal 'A' No Pulses - AutoCodes.com — P0374 Code - Timing Reference High Resolution Signal 'A' No Pulses

What does this mean?

What are the Possible Causes of the DTC P0374?

Timing Reference Optical Sensor harness is open or shorted
Timing Reference Optical Sensor circuit poor electrical connection
Faulty Timing Reference Optical Sensor
Damaged Powertrain Control Module (PCM)

How to Fix the DTC P0374?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0374 code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P0374 code?

Need more information on how to fix the P0374 code? Get Access to Factory Service Manuals

Need Help with the Code?

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Information for Specific Makes

P0374 Mercedes-Benz — Timing Reference High Resolution Signal 'A' No Pulses

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0374 Code

No Frequently Asked Questions about P0374 Code found.

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Flash Drive 5610
Date: January 31, 2026 at 8:38 pm

Jan 2026, 2004 3500 Duramax Diesel, LLY 131,000 mi. pulled code P0374 after 45 minutes idling engine symbol appeared. Cut truck off, tried starting it, it shut right off, tried two more times same result. Grabbed OBD scanner, Got P0374 & P0700 codes. Cleared them. It started right up. Drove Next day replaced with New primary battery. Stopped at Diesel repair shop, they confirmed that might have been the problem, it should be fine now.

Reply to Comment
- OBDIITech
  Date: February 2, 2026 at 9:11 pm
  
  On the LLY Duramax, P0374 means the ECM lost the high-resolution timing signal from the injection pump / crank reference. When that signal drops out, the engine will usually stall or start and die exactly like you described. The P0700 just means the transmission module saw a major engine fault and flagged it.
  
  Low system voltage can absolutely trigger this. These trucks are very sensitive to battery condition, especially after long idle time. If voltage drops or gets noisy, the ECM can lose the timing signal even though the sensor itself is fine. Replacing a weak battery was a good move.
  
  That said, I’d treat it as “possibly fixed,” not guaranteed fixed yet.
  
  If the batteries were mismatched, old, or one was dragging the other down, that can cause intermittent voltage dips. On a Duramax you really want both batteries healthy and matched. Also check:
  
  • Both battery cables and grounds (frame + engine grounds)
  • The junction block connections
  • Alternator output under load
  • Harness near the crank / pump sensor for rubbing or oil contamination
  
  If it was purely voltage-related, the truck will run normally and the code won’t return. If P0374 comes back, then you’d start suspecting the crank reference wiring or sensor circuit.
  
  For now, drive it and monitor. One event after a long idle with a weak battery is believable. Repeated events mean you dig deeper.
  
  The key thing: you did the right first repair. Just keep an eye on it.
  
  Reply to Comment