P2987 – Reductant Injector “C” Control Circuit Low

System: Powertrain | Standard: ISO/SAE Controlled | Fault type: Circuit Low | Location: Designator C

Definition source: SAE J2012/J2012DA (industry standard)

DTC P2987 indicates the powertrain control module has detected a “circuit low” condition in the control circuit for Reductant Injector “C.” In practical terms, the module is seeing an unexpectedly low electrical signal on the injector’s control side when it commands the injector on or off, or when it checks the circuit’s integrity. This is an electrical fault classification, not a confirmed mechanical injector failure. The exact injector labeling (what “C” refers to), wiring layout, and the conditions required to set the code can vary by vehicle, so always confirm connector pinouts, circuit routing, and test criteria using the correct service information for the specific platform.

What Does P2987 Mean?

P2987 – Reductant Injector “C” Control Circuit Low means the vehicle has detected a low-input electrical condition in the control circuit that operates reductant injector “C.” Under SAE J2012 DTC conventions, “circuit low” faults generally point to the control signal being pulled lower than intended during monitoring. Typical electrical interpretations include a short-to-ground, an open on the power/feed side that prevents the signal from reaching its expected level, excessive resistance causing voltage drop under load, or a driver/control circuit that cannot maintain the commanded state. The code identifies the affected circuit path; it does not, by itself, prove the injector is mechanically stuck or that fluid delivery is correct.

Quick Reference

• Subsystem: Reductant injector “C” electrical control circuit (injector actuator control within the reductant dosing system).
• Common triggers: Control circuit signal pulled low due to short-to-ground, open feed, high resistance, or poor connection while the module is commanding/monitoring the injector.
• Likely root-cause buckets: Wiring/connector issues, power/ground delivery problems, injector coil/actuator electrical fault, control module driver circuit concerns.
• Severity: Typically moderate; may lead to emissions system malfunction and potential torque reduction or warning indicators depending on strategy.
• First checks: Visual harness/connector inspection, check for corrosion/water intrusion, verify power/ground integrity, inspect for chafing near heat sources, confirm correct connector seating/pin fit.
• Common mistakes: Replacing the injector first without confirming a circuit-low cause (short-to-ground, feed open, or voltage drop under load).

Theory of Operation

A reductant injector is an electrically actuated dosing device controlled by the powertrain controller. Depending on design, the module may supply power and switch the ground (low-side control) or supply ground and switch the power (high-side control). The controller commands dosing by pulsing the injector and monitors the control circuit’s electrical behavior to confirm the circuit can be driven and responds as expected.

For a “control circuit low” fault, the controller detects the control signal is lower than expected for the commanded state, or it fails an integrity check that expects the circuit to pull to a higher level when not being pulled low. Common electrical reasons include a short-to-ground on the control wire, an open or high-resistance feed that prevents the circuit from rising, or excessive resistance at terminals causing a loaded voltage drop during injector actuation.

Symptoms

• Warning light: Malfunction indicator lamp or powertrain warning illuminated.
• Messages: Emissions/aftertreatment-related warnings depending on vehicle strategy.
• Reduced power: Torque limitation or reduced-performance mode on some platforms.
• Poor drivability: Hesitation or derate-like behavior that correlates with aftertreatment faults (varies by vehicle).
• Stored codes: Additional reductant system or injector circuit DTCs may be present.
• Failed monitor: Readiness/monitor status for aftertreatment may not complete until the fault is corrected.

Common Causes

• Short-to-ground in the Reductant Injector “C” control circuit wiring harness
• Open power/feed to the reductant injector driver circuit (resulting in a low electrical state at the control circuit)
• High resistance in the control circuit (corrosion, damaged conductor, poor splice) causing excessive voltage drop
• Poor connector contact at the injector, inline connector, or control module (spread pins, corrosion, incomplete seating, terminal push-out)
• Reductant injector “C” internal electrical fault (coil/solenoid issue) pulling the circuit low or loading the driver abnormally
• Shared ground or power distribution issue affecting the reductant injector circuit (ground eyelet, fuse feed, junction)
• Water intrusion or contamination at connectors leading to conductive paths to ground and low signal behavior
• Control module driver/output stage fault for injector “C” (less common; confirm with circuit tests first)

Diagnosis Steps

Tools typically needed include a scan tool with data logging and bi-directional controls (if supported), a digital multimeter, and a wiring diagram/service information for the correct connector pinouts (varies by vehicle). A back-probing kit and basic terminal inspection tools are helpful. If available, use a breakout lead to avoid damaging terminals during testing.

1. Confirm the DTC and capture freeze-frame: Verify P2987 is present and record freeze-frame and related codes. Note whether the fault is current or history, and whether any power supply or ground-related DTCs are also stored.
2. Check readiness and repeatability: Clear codes, then run the applicable enable conditions (varies by vehicle) to see if P2987 returns immediately or only under certain operating conditions. This helps separate hard faults from intermittent wiring issues.
3. Perform a focused visual inspection: Inspect the harness and connectors for the reductant injector “C” circuit. Look for chafing, pinched wiring, melted insulation, recent repairs, or routing too close to heat sources. Closely inspect connector locks, seals, and any signs of moisture or crystallized residue.
4. Connector and terminal integrity checks: With the circuit powered down as required by service information, disconnect the injector and related connectors. Check for bent/spread terminals, corrosion, terminal push-out, or poor pin fit. Correct any mechanical connector issues before electrical testing.
5. Wiggle test while monitoring data: Reconnect as appropriate and monitor scan tool data and DTC status while gently wiggling the harness at the injector, along the run, and near the module connector. If the fault toggles with movement, prioritize locating the exact harness/connector location causing the low input condition.
6. Check for short-to-ground on the control circuit: With connectors disconnected as directed (to isolate the circuit), use a multimeter to test the control wire for unintended continuity to chassis ground. A short-to-ground is a primary cause of a “circuit low” result; if found, trace and repair the harness damage or contamination path.
7. Verify power/feed and ground paths with voltage-drop testing: Under loaded conditions (command the injector if bi-directional control is available, or use the applicable functional test per service info), perform voltage-drop checks on the power supply and ground paths feeding the injector circuit. Excessive drop indicates high resistance at a fuse, relay, splice, ground point, or connector.
8. Assess injector electrical loading: With the injector disconnected, check the injector for an internal electrical fault using the test method specified in service information (exact criteria vary by vehicle). If the injector is internally shorted or otherwise abnormal, it can pull the control circuit low and trigger the monitor.
9. Command test (if supported) and compare behavior: Use the scan tool’s output controls to command reductant injector “C” on/off while observing the control circuit response (using scan data and/or meter checks at the appropriate pins). Compare behavior to a known-good injector channel if the system design allows comparison on the same vehicle.
10. Isolate module vs wiring: If the harness tests good (no short-to-ground, acceptable voltage drop, connectors solid) but the circuit still indicates low when commanded/monitored, isolate the module side per service information. If the low condition persists only with the module connected, suspect a driver/output issue only after all external causes are eliminated.
11. Repair, recheck, and validate: After repairs, clear codes, run the applicable drive cycle/functional test, and confirm P2987 does not return. Review logged data to ensure the condition does not reappear during vibration, temperature changes, or under the same operating conditions captured in freeze-frame.

Professional tip: Prioritize finding an unintended path to ground and verifying loaded power/ground integrity. Many “circuit low” faults look normal with a simple unplugged resistance check, but reveal themselves during a voltage-drop test with the circuit commanded on. When the code is intermittent, a structured wiggle test combined with live-data logging is often the fastest way to pinpoint the exact section of harness or connector that is intermittently pulling the control circuit low.

Possible Fixes & Repair Costs

Repair cost for P2987 varies widely because the code only indicates a low electrical condition in the Reductant Injector “C” control circuit, not a confirmed failed part. Total cost depends on pinpoint testing results, access/packaging, parts replaced, and labor time.

• Repair wiring damage in the reductant injector “C” control circuit (chafed insulation, pinched harness, melted sections) found during inspection and continuity checks
• Clean, reseat, or replace connector terminals for the injector or harness connector if corrosion, moisture intrusion, poor pin fit, or fretting is verified
• Correct power/feed issues supplying the injector circuit (blown fuse, faulty relay, poor splice, high-resistance feed) confirmed by voltage-drop testing
• Restore ground integrity if the injector driver ground path or shared ground is loose/high resistance (clean and tighten ground point, repair broken ground conductor)
• Replace the reductant injector “C” only after electrical checks show the injector is the source of the low condition (for example, an internal short lowering control circuit voltage)
• Repair harness routing and retention to prevent recurrence if movement/heat/vibration is causing intermittent shorts-to-ground
• Module-side circuit repair or module replacement only if service information and testing confirm a failed driver/control circuit and all external wiring/components test good

Can I Still Drive With P2987?

You may be able to drive, but it depends on how the vehicle manages emissions-related faults and whether the low circuit condition is continuous or intermittent. A reductant injector control problem can lead to reduced emissions performance and may trigger warning indicators or a limited operating strategy. If the vehicle shows reduced power, severe drivability changes, multiple warning messages, or any safety-related symptoms (such as stalling or loss of propulsion), do not drive—stop and diagnose the circuit fault first.

What Happens If You Ignore P2987?

Ignoring P2987 can allow an electrical short-to-ground, open feed, or high-resistance connection to worsen over time, potentially causing intermittent operation to become a hard fault. Continued operation may result in persistent warning lights, emissions non-compliance, possible performance limitations depending on vehicle strategy, and increased likelihood of additional codes related to the reductant dosing system due to repeated monitor failures.

Related Reductant Injector Codes

Compare nearby reductant injector trouble codes with similar definitions, fault patterns, and diagnostic paths.

• P2991 – Reductant Injector “D” Control Circuit Low
• P2057 – Reductant Injector Circuit Low Bank 2 Unit 2
• P2054 – Reductant Injector Circuit Low Bank 1 Unit 2
• P2051 – Reductant Injector Circuit Low Bank 2 Unit 1
• P2048 – Reductant Injector Circuit Low Bank 1 Unit 1
• P2908 – Exhaust Aftertreatment Fuel Injector Circuit Low

Key Takeaways

• P2987 indicates a low electrical condition in the Reductant Injector “C” control circuit, not a guaranteed bad injector.
• Most root causes fall into wiring/connector, power feed, or ground integrity problems that pull the circuit low.
• Confirm the fault with test-driven diagnostics (voltage-drop, short-to-ground checks, connector inspection) before replacing parts.
• Driving impact varies by vehicle, but persistent faults can lead to warnings and operating limitations.
• Fixing the underlying electrical issue early helps prevent repeat failures and additional related codes.

Vehicles Commonly Affected by P2987

• Diesel-equipped vehicles using a reductant dosing system for aftertreatment
• Light-duty trucks and vans with electronically controlled reductant injection
• Medium-duty applications where harness routing is exposed to heat and vibration
• Vehicles operated in corrosive environments where connectors are prone to moisture intrusion
• High-mileage vehicles with aging insulation, brittle conduit, or loosened grounds
• Vehicles with recent underbody repairs where the harness may be misrouted or pinched
• Vehicles used for frequent short trips where repeated thermal cycling can stress connectors and terminals
• Vehicles with prior wiring modifications that introduce splices, poor grounds, or incorrect repairs near the dosing system

FAQ

Does P2987 mean the reductant injector “C” is bad?

No. P2987 only indicates the control circuit is being seen as low by the control module. That can be caused by a short-to-ground, an open power/feed, high resistance in wiring or connectors, poor ground integrity, or (less commonly) an internal injector fault. Testing is required to confirm the failed element.

What electrical problems most commonly create a “circuit low” condition?

Typical “circuit low” causes include a short-to-ground on the control wire, a rubbed-through harness contacting metal, water intrusion in a connector bridging terminals, an open or weak power supply to the circuit, or high resistance that creates excessive voltage drop under load.

Can a blown fuse or relay issue set P2987?

Yes, depending on vehicle design. If the injector circuit’s power/feed is lost due to a fuse, relay, or feed splice problem, the module may interpret the resulting signal behavior as a low condition. Always verify feeds and grounds with service information and voltage-drop testing rather than assuming the injector is the issue.

Will clearing the code fix P2987?

Clearing the code only resets stored fault information; it does not repair the underlying low circuit condition. If the problem is still present, the monitor will typically fail again and the code will return. Clearing can be useful after repairs to confirm the fix during a controlled road test and recheck.

What should I check first if P2987 appears intermittently?

Start with a close inspection of the harness and connectors at the injector and along the routing for rub-through, loose pin fit, moisture, and corrosion, then perform a wiggle test while monitoring live data or circuit status (varies by vehicle). Intermittent lows are often caused by movement-related shorts, poor terminal tension, or high-resistance connections that worsen under vibration.

Verify all test procedures and connector pinouts in the correct service information for your vehicle, since circuit design, terminal identification, and control strategy vary by platform.