OBD-II trouble code
P0379: Timing Reference High Resolution Signal 'B' No Pulses
The second timing reference has gone completely silent. Unlike a dead primary reference, this fault frequently ends at a module rather than a sensor — and the engine may still be running while you diagnose it.
Quick facts
- System
- Powertrain
- Category
- Sensors / Timing
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $150 – $1,600
- DIY difficulty
- Advanced DIY
What does P0379 mean?
P0379 is the last member of the high-resolution timing family and the hard-failure member of the 'B' channel: the module expected a stream of fine timing pulses on the second reference and received nothing at all. Not a distorted signal, not a dropout — silence.
What separates this code from its 'A' channel counterpart is where the silence points. When the primary reference dies, the prime suspect is the pickup itself, because the primary is almost always a physical sensor reading a wheel. The 'B' reference often is not. On many platforms — heavy diesels are the textbook case — the second reference is a conditioned copy of the crank signal that one module generates and transmits to another, typically from the engine controller to a separate fuel injection control module. A copy cannot go silent because a reluctor wheel stopped turning; the engine is demonstrably turning if 'A' is still reporting. Total silence on a relayed copy indicts exactly three things: the output stage of the module that sends it, the wire that carries it, or the input stage of the module that receives it. Two of those three are modules. That makes P0379 the member of this family most likely to end in a control unit rather than a sensor, and the diagnosis should be run with that expectation rather than against it.
The presence of a healthy 'A' channel is not just a comfort — it is the most valuable measurement you get, and it costs nothing. It proves the crankshaft is turning, the reference wheel is intact, and any supply and ground the two channels share are alive. Every one of the expensive mechanical explanations is eliminated before a meter comes out. What is left is the private portion of the 'B' path, which on most architectures is one wire and two module pins.
How the vehicle behaves depends entirely on what consumes the 'B' reference. Where it feeds a separate injection controller, that controller has just lost its only timing source, and the result is a dead bank, a no-start, or a stall with no restart. Where 'B' exists as a redundant cross-check, the engine can run indistinguishably from normal — and that normal-running engine is itself a diagnostic finding, because it tells you the consumer of the missing signal was never critical on this platform. Read the symptom as evidence, not as reassurance.
Common causes
- Failed output driver in the module that generates and transmits the duplicated timing reference
- Broken, chafed or disconnected wire in the dedicated run between the sending and receiving modules
- Backed-out terminal or corrosion at either end of the inter-module reference line
- Failed input circuit in the receiving module, most commonly a separate fuel injection control module
- Completely failed second pickup on the minority of engines where 'B' is a genuine standalone sensor
- Blown reference-circuit supply where the second sensor has its own feed
- Unplugged connector left off after unrelated service work near the bellhousing or injection pump
- Replacement module installed without the programming that enables the retransmitted reference output
Symptoms
- Check engine light with an engine that starts and drives entirely normally on redundancy architectures
- No-start or crank-no-start where the second reference feeds a dedicated injection controller
- One dead cylinder bank on split-bank injection systems
- Stall followed by no restart, with the code stored as a hard fault rather than intermittent
- Module communication codes stored alongside this one when a shared connector is at fault
- Reduced power or a fixed limp strategy on systems that derate after losing the cross-check
Diagnostic steps
- 1.Pull codes from every module, not just the engine controller. If a separate injection control module exists, its stored faults tell you immediately whether it is the receiver that lost the signal.
- 2.Confirm the 'A' channel is clean. A healthy primary reference proves the crank is turning and the wheel is intact, which strips the mechanical causes off the list before any measurement.
- 3.Establish from the wiring diagram whether 'B' on this platform is a real second pickup or a retransmitted copy. The answer divides the remaining work in half.
- 4.On a relayed-copy system, scope the sending module's output pin with the engine cranking or running. Pulses present here move the fault down the wire; a flatline here condemns the sender's output stage.
- 5.If pulses leave the sender, scope the receiver's input pin. Signal in, nothing acknowledged means the receiving module's input circuit — but verify its power and ground before condemning it.
- 6.Inspect the full length of the inter-module run for crush points, previous repairs and added accessories. A single dedicated wire that passes near service areas is a common casualty of earlier jobs.
- 7.On genuine two-sensor engines, test the 'B' pickup as you would any crank sensor: resistance against specification for a magnetic unit, supply and switching test for a Hall type.
- 8.After any module replacement, confirm the programming step that enables the reference output was actually performed — an unprogrammed sender reproduces this code exactly.
Repair cost
$150 – $1,600
A repaired inter-module wire or connector runs $150 to $500 including the diagnostic time to isolate it. A genuine second sensor, where fitted, is $40 to $200 in parts and $150 to $500 installed. The expensive endings are the modules: a failed sender or receiver is $600 to $1,600 with programming, and because this is the family member most likely to finish there, insist on the scope test at both ends of the line before any module is purchased. Silence at the output pin is the evidence that justifies that bill; without it, the module is a guess.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with control module replacement and programming preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.