🚨 Diagnostic Profile
Vehicle Make: Chrysler
Description: Secondary Air Injection System Relay A Control Circuit High. The secondary air injection (AIR) system uses an electric air pump, check valve, and control valves to inject fresh air into the exhaust during cold start to reduce emissions. This fault indicates the powertrain control module (PCM) has detected the AIR pump relay control circuit reading above its expected range. This description is commonly associated with DTC P0418, but the specific code and sub-type must be verified against the vehicle’s model year and engine.
🚨 Repair Difficulty Tier
Tier: [Intermediate]
The relay itself is typically accessible and inexpensive, but diagnosing a high control circuit condition requires a multimeter, wiring access, and scan tool data. The relay, its fuse, and circuit wiring may be shared with other systems, so proper isolation is required to avoid misdiagnosis.
🛠️ Resolution Steps
Step 1: Preliminary Inspection
- Confirm the DTC is current and not history-only using a scan tool, and record any freeze frame data including engine coolant temperature at the time the fault set, since the AIR system is a cold-start emissions strategy.
- Inspect the AIR pump relay location: on most Chrysler/Jeep/Dodge applications the relay is housed in the underhood Power Distribution Center (PDC/IPM); confirm exact cavity position using the label molded into the underside of the PDC cover lid for the specific model year.
- Check the relay fuse and the relay socket for corrosion, heat damage, melted terminals, or loose connections.
- Inspect the AIR pump harness and connector at the pump and relay for chafing, damage, or water intrusion, paying particular attention to routing near the exhaust manifold heat shield where thermal damage is common.
- Check the AIR pump, check valve, and hoses for physical damage, blockage, carbon buildup, or disconnection.
Step 2: Diagnostic Verification
- Command the AIR pump relay on and off with a bidirectional scan tool, if supported, and listen/feel for relay click and pump operation to confirm mechanical function.
- With the key on engine off and the relay removed, back-probe the PCM-side control circuit terminal in the relay socket using a digital multimeter referenced to a verified good chassis ground. A “Control Circuit High” fault typically means the PCM, which pulls the control circuit low (near 0V) to energize the relay, is instead seeing battery or reference voltage on that circuit when it should be grounded — this points to either a short to voltage/power feed within the harness, or an open/high-resistance condition in the PCM’s internal ground-side driver path.
- Check for a short to voltage in the relay control circuit by disconnecting the PCM connector (ignition off) and measuring resistance/continuity from the control circuit terminal to chassis ground and to battery voltage sources; compare findings against factory wiring diagrams for the specific model year and engine to confirm expected open-circuit readings.
- Test the relay coil resistance and switched-contact continuity with a multimeter or dedicated relay tester; a typical automotive micro-relay coil reads several dozen to a few hundred ohms, but confirm against the relay’s stamped specification or factory service data rather than assuming a fixed value.
- With the relay reinstalled, command the AIR pump on and verify current draw and ground path integrity at the pump connector using an inductive amp clamp or multimeter in series, per the service manual load-test procedure.
- Clear codes and perform a cold-start verification drive cycle (the AIR system only runs briefly after a cold start), then recheck with the scan tool for return of the fault or a completed AIR system monitor.
Step 3: Resolution & Reset Process
- Replace the AIR pump relay if it fails the coil resistance or contact continuity test, or repair the control circuit wiring at the identified fault location (chafe point, pinched wire, or corroded splice) if an open, short, or high-resistance condition is confirmed.
- Replace any damaged connectors, fuses, or check valves found during inspection; if the pump itself fails the current draw/load test, replace the AIR pump assembly per OEM procedure.
- Clear all stored DTCs with a scan tool and confirm the AIR system monitor runs to completion during a cold-start drive cycle (monitor will not run on a warm engine).
- Confirm there are no pending or stored codes on a follow-up scan and document the repair, including part numbers, measured resistance/voltage values, and drive cycle results.
📦 Parts, Labor, and Budget Estimates
Required Components/Software:
- AIR pump relay (OEM Mopar micro-relay, verify exact part number against VIN at dealer parts counter or OEM parts catalog)
- Relay fuse (if damaged) — amperage rating must be confirmed from the PDC fuse/relay diagram for the specific model year
- Connector pigtail or harness repair kit (if chafed/corroded wiring is found) — universal weatherproof splice kit or OEM pigtail depending on damage location
- Secondary air injection check valve, pump-to-manifold hose, or AIR pump assembly (only if failed during load test)
- Scan tool with bidirectional control capability (e.g., OEM-level StarMOBILE/wiTECH for Chrysler/Dodge/Jeep/Ram, or an aftermarket tool with verified bidirectional AIR system support) and current software calibration
Average Component Price:
- AIR pump relay: approximately $15–$45 (OEM Mopar relay)
- Fuse and connector/splice materials: approximately $5–$30
- AIR pump assembly (if required): approximately $150–$450 depending on model; check valve or hose only: approximately $30–$100
- Total estimated parts range: approximately $20–$500 depending on whether the fix is limited to the relay/fuse or extends to pump/check valve replacement
Estimated Labor Hours:
- Preliminary inspection and scan data review: approximately 0.3–0.5 hour
- Diagnostic verification and circuit testing (relay, wiring, and load test): approximately 0.5–1.2 hours
- Relay replacement or wiring repair and verification drive cycle: approximately 0.3–0.8 hour (add 0.8–1.5 hours if full AIR pump assembly replacement is required due to limited access on some engine layouts)
- Total shop book time (per service information): approximately 1.0–2.5 hours for relay/wiring repair; up to 3.5 hours if pump replacement is necessary — confirm exact book time against Chrysler/Mopar flat-rate guide for the specific model year and engine