OBD-II trouble code
P0376: Timing Reference High Resolution Signal 'B' Too Many Pulses
Extra edges on the second timing channel. Because 'B' usually travels the long way round the engine bay, this is a noise problem far more often than a hardware one.
Quick facts
- System
- Powertrain
- Category
- Sensors / Timing
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $120 – $1,600
- DIY difficulty
- Advanced DIY
What does P0376 mean?
P0376 sets when the count on the second high-resolution channel comes back higher than the engine can produce. What makes it a different job from the equivalent fault on channel 'A' is geography.
The 'B' reference is the one that travels. Where it is a relayed copy, it runs from one module's output pin to another module's input pin, which on most installations means a length of wire crossing the engine bay or running down the side of the block. Where it is a genuine second pickup, it is usually the one on the far bank, which means its lead is the longer of the two by some margin. Either way, the 'B' path spends more of its life bundled alongside things that switch large currents — injector drivers, glow plug or intake heater feeds, the alternator cable, starter wiring. A long conductor running next to switched high current is the textbook recipe for coupled interference, and coupled interference on a pulse-counting line reads as extra pulses.
That is why the suspect list here leans electrical in a way that channel 'A' does not. On a relayed-copy system there is no reference wheel in the 'B' path at all, so debris on a magnetic pickup tip — a leading cause of extra pulses on 'A' — is simply not available as an explanation. Working out which architecture applies eliminates whole categories of cause before any testing begins.
This code also has access to the single most powerful diagnostic tool in the family, and it is one that channel 'A' cannot use alone. Put both references on a two-channel scope, triggered together, and look at them side by side. If the extra edges appear on 'B' and 'B' only, the fault is downstream of whatever the two channels have in common — the run, a connector, a driver, a receiver. If both channels carry the same extra edges, the problem is upstream at the shared source, the shared supply or the shared ground, and chasing the 'B' wiring will find nothing. One capture, and half the possibilities disappear.
One cause is worth naming plainly because it is specific to the platforms that use this architecture. The inter-module reference line is a favourite tapping point for aftermarket tuning boxes, injector timing modules and speed-signal devices, all of which splice into a signal that was designed to be left alone. A splice adds a stub, a stub is an antenna, and the module counts what the antenna collects. If anything has been added to the vehicle's engine wiring, disconnect it and retest before ordering parts.
Common causes
- Interference coupled onto a long inter-module reference wire running alongside injector, heater or charging cables
- Aftermarket tuning module, timing box or signal device spliced into the reference line between modules
- Damaged or missing cable shield along the run, or a shield grounded at both ends
- Poor ground at the receiving module allowing noise to appear as signal at its input
- Chafed reference wire intermittently contacting an adjacent switched circuit
- Failing alternator putting AC ripple onto the system and onto the reference line with it
- Failed output driver in the sending module producing double edges or ringing on each transition
- Debris on the tip of the second pickup where 'B' is a genuine separate sensor rather than a relayed copy
Symptoms
- Check engine light on, sometimes with no obvious driveability complaint
- Rough running or misfiring confined to one cylinder bank on split-bank injection systems
- Stumbling or surging that changes when a heavy electrical load switches on
- Reduced power as the receiving controller adopts a protected strategy
- Correlation or plausibility codes stored alongside this one
- Hard starting or stalling on systems where the injection controller depends solely on this reference
Diagnostic steps
- 1.Determine from the wiring diagram whether 'B' is a relayed copy travelling between modules or a genuine second sensor. On a relayed system there is no reference wheel in this path, which removes an entire class of cause immediately.
- 2.Put both timing references on a two-channel scope triggered together. Extra edges on 'B' alone point downstream of the shared source; extra edges on both point upstream at the shared source, supply or ground.
- 3.Inspect the whole reference run for splices, taps and added modules. Tuning boxes and timing devices commonly tap this exact line, and a splice stub behaves as an antenna.
- 4.Disconnect any aftermarket device found on the engine wiring and retest before ordering parts.
- 5.Trace the physical route of the reference wire and note where it runs close to injector drivers, heater feeds, the alternator cable or starter wiring. Proximity to switched high current is the cause you are looking for.
- 6.Check the cable shield along the whole run and confirm it is intact and grounded at one end only.
- 7.Test the receiving module's ground with a voltage drop measurement. A module referencing a poor ground sees noise where a properly grounded one would see nothing.
- 8.Test the alternator for AC ripple so a whole-vehicle noise source is ruled out before the harness is opened up.
- 9.Scope at the sending module's output pin. Ringing or double edges leaving the module means the driver has failed and the wiring is innocent.
Repair cost
$120 – $1,600
Removing an aftermarket device that was tapping the reference line can cost nothing beyond the $120 to $250 diagnostic charge. Repairing a chafed wire, restoring a shield or cleaning up a corroded module ground is $150 to $500, with most of that being the time spent finding it rather than the fix itself. An alternator replaced for ripple is $350 to $800. Where 'B' is a real second sensor, $150 to $500 fitted, allowing for the far-bank access. A failed module output driver or input stage is the top of the range at $600 to $1,600 including programming, and should not be quoted until the wiring between the two modules has been proven good.
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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.