Begin troubleshooting with the fuse box layout–located under the driver-side dashboard panel. Pin F37 and F40 handle primary power distribution for auxiliary lighting and emergency systems. Verify continuity with a multimeter before proceeding to deeper diagnostics. Failures in these circuits often mimic dead batteries, leading to misdiagnosed alternator issues.
Trace the CAN bus network using the powertrain control module (PCM) schematic as the anchor point. Black/red wires denote high-speed CAN-H (pin A147), while blue/yellow identify CAN-L (pin A148). Corrosion at the splice sites under the front passenger seat is a known failure point–inspect for green oxide buildup or frayed insulation before replacing modules.
For lightbar integration, follow the yellow/light-blue wire from the B+ terminal (fused at 60A) to the auxiliary relay bank (mounted near the rear liftgate). The S955 splice cluster often overheats; bypass it with 10-gauge silicone wire if resistance exceeds 0.2 ohms. Replace the factory ground strap (bolt G101) if showing resistance above 0.1 ohms.
Isolate starter solenoid failures by testing voltage drop across the purple/white wire (pin 50) during cranking. Voltage below 9.6V indicates a worn ignition switch or corroded bulkhead connector–clean terminals with deoxIT D5 before resorting to replacement.
For HVAC diagnostics, refer to the secondary fan control circuit (dark-blue wire, pin C167). The blower motor resistor (located behind the glove box) frequently burns out under sustained high-load operations–replace with a 40A relay retention kit to extend lifespan. Verify the low-pressure AC switch (grey/light-green wire) before condemning the compressor.
Electrical Schematics for the 2016 Model Year Law Enforcement SUV
Begin troubleshooting by locating fuse F38 (15A) in the central junction box, which supplies power to the rear door locks and liftgate module. Verify continuity between pin 32 of the GEM (Generic Electronic Module) and the liftgate latch actuator using a multimeter set to 200Ω. Resistance should read below 5Ω; readings above 15Ω indicate corroded terminals in connector C153.
For the auxiliary power outlets, check relay R12 in the battery junction box–it controls the 12V rear console socket. Swap R12 with a known-good relay (e.g., R10 for the horn) to isolate failure. If the outlet still doesn’t activate, inspect wiring harness W47 for chafing near the left rear wheel well, a frequent failure point due to road debris exposure.
| Component | Connector | Pin | Wire Color | Expected Voltage (KOEO) |
|---|---|---|---|---|
| Blower Motor | C32 | 2 | OR/LG | 11.5–12.6V |
| HID Headlamp (Low Beam) | C142 | 5 | YE/VT | 13.2–14.8V |
| PCM Power Relay | C113 | 30 | WH | Battery Voltage |
When diagnosing the 150A alternator, measure voltage at terminal B+ with the engine running–it should stabilize at 14.0–14.5V. If readings fluctuate erratically, replace the voltage regulator integrated into the alternator housing rather than attempting repairs on individual diodes. The drive belt (PN YL3Z-8620-AA) must maintain tension between 120–150 lbs; adjust the automatic tensioner if deflection exceeds 0.5 inches.
The heated windshield grid requires a dedicated 50A fuse (F102) in the auxiliary relay box. If the grid fails partially, test individual horizontal strands for continuity–they should register below 10Ω. Strand breaks typically occur 4–6 inches from the lower edge, where ice buildup is most common. Use a conductive paint kit (3M 08878) for repairs, applying three thin layers with a 30-minute cure time between each.
For the trailer tow electrical system, confirm the 7-way connector at the rear receives power from fuse F22 (30A). Pin C (auxiliary power) should deliver 12V when the ignition is in the RUN position. If voltage is absent, trace the pink/black wire to splice S132 near the rear bumper–look for pinched wires where the harness exits the vehicle frame.
Critical sensors like the throttle position sensor (TPS) and mass air flow (MAF) sensor share ground via the chassis ground point G101. Clean G101 with a stainless steel brush if voltage drop exceeds 0.2V during cranking. The MAF sensor’s signal wire (VT/OG) should oscillate between 0.5V (idle) and 4.0V (wide-open throttle) when monitored with an oscilloscope; flat-lined readings mandate sensor replacement.
Finding the Central Power Distribution Hub and Control Module Layouts
Start by removing the lower dash trim panel on the driver’s side – it’s secured with four 8mm bolts and two plastic clips. Behind it, you’ll expose the primary junction block, marked with a white label reading “F2” or “BJB” (Battery Junction Box). This cluster contains high-current links for the cooling fan, ignition coils, and high-beam relay, all outlined in the service manual’s Section 501-14.
The secondary relay panel sits beneath the passenger-side glovebox, accessible after popping the two 7mm screws and swinging the compartment downward. Look for the rectangular black module with seventeen socket positions; the top row handles transmission control, rear defrost, and blower motor circuits, while the lower tier manages door locks and A/C clutch engagement. A 30-amp maxi-fuse labeled “Horn” is the third slot from the left.
Trace the thick red cable from the positive battery terminal–it terminates at the BJB’s main input stud. This connection branches into three 10-gauge feeds: one to the starter solenoid, another to the alternator field coil, and the third to the central fuse distribution strip. Use a 1,000-amp fuse puller to safely extract the 120-amp mega-fuse protecting the entire network before probing downstream circuits.
Behind the instrument cluster, a hidden connector (C2300) routes signals to the powertrain control module. Pin assignments follow a color-coded scheme: purple/white wires carry TPS data, orange/black handles VSS input, and green/red transmits fuel level readings. Probe these with a DVOM set to 20V DC; expect 0.5–4.5V on sensor lines under normal operation.
For climate control diagnostics, locate the grey 16-pin connector beneath the radio bezel. Pin 9 (white/violet) carries cabin temperature sensor feedback, while pin 13 (yellow/green) delivers blend door actuator control. Disconnect the harness, then verify 5V reference voltage on pin 16 – absence suggests a shorted sensor or fractured trace on the HVAC circuit board.
Under the rear cargo floor, a compact fuse/relay box manages trailer tow functions. The leftmost 40-amp fuse protects the auxiliary power outlet; if tripped, inspect the orange wire leading to the socket for chafing against the frame. The adjacent solid-state relay switches backup camera power, energizing only when the transmission selector engages reverse.
Front fog lamp circuits route through a dedicated 20-amp fuse in the under-hood box. Brown/light-blue wires exit the halogen bulb sockets, terminating at the multifunction switch via connector C303b. Test continuity by unplugging the harness and probing the terminals–open circuits indicate corroded contacts or a severed ground strap beneath the left-front fender liner.
Verifying Signal Integrity on Safety Systems
Airbag squib resistance must read 2–3 ohms on diagonal pairings (driver/passenger and left/right curtain). Exceeding 5 ohms triggers a diagnostic trouble code; replace the spiral cable assembly if readings fluctuate during steering wheel rotation. Stability control steering angle sensor calibrates at connector C175 (grey/red and grey/yellow wires), delivering a 0.25V center position signal–verify with a scope while rotating the wheel ±90 degrees.
Power Flow Analysis for Vehicle Illumination and Emergency Circuits
Locate the central junction box beneath the instrument panel on the driver’s side–identified by a black plastic cover secured with two T25 Torx screws. Remove the cover to expose fuse positions F34 (30A, high-beam relay), F41 (20A, headlamp control), and F55 (10A, emergency lighting). Use a multimeter set to DC voltage; probe the input side of each fuse while toggling the corresponding switch on the dash. A reading below 11.8V indicates a corroded splice or broken feed at joint C307, located behind the left kick panel.
Follow the red/green striped conductor from fuse F41 to the headlamp switch. Trace the cable loom along the firewall, securing it at harness clip H23 with a nylon tie to prevent chafing against the vacuum reservoir. At connector C282, verify pin B8 carries 12.6V when the switch is in the “on” position. If voltage is absent, inspect the 120Ω resistor inline between the switch and relay coil–desolder and replace if carbon tracks are visible.
Relay Behavior and Ground Path Integrity
Test relay R2 (headlamp high-beam) by swapping it with R5 (horn) of identical part number. If the horn functions but high beams do not, remove the relay and apply 12V directly to pins 85 and 86 using a fused jumper wire. An audible click confirms the coil is intact; failure to click indicates a faulty relay or open circuit. Check pin 30 for battery voltage–corrosion at terminal block TB104 often disrupts this feed.
Emergency strobe circuits route through dedicated tie-bar splice S6, fed from fuse F55. At connector C127 beneath the rear cargo area, confirm pin A2 delivers uninterrupted 14.2V during engine operation. Use a 47kΩ pull-down resistor across pins A2 and A3 to rule out floating voltage caused by a compromised ground at G401, a sand-cast aluminum stud near the rear hatch hinge.
Load Distribution and Fault Mitigation
Attach an oscilloscope to the blue/white conductor feeding the LED lightbar at splice S7-3. A jagged pattern exceeding 0.7V peak-to-peak signifies pulse-width modulation interference–wrap the conductor in copper tape and relocate it away from the fuel pump power line. For intermittent taillight failures, replace the 3Ω current-limiting resistor near bulb socket L12; thermal cycling causes solder cracks visible under magnification.
Isolate the auxiliary power module by disconnecting connector C99 at the rear seat release switch. Measure resistance between pin C8 and chassis ground–values above 2Ω warrant cleaning the M6 bolt at G303 with a wire brush and reapplying dielectric grease. Reassemble with zinc-plated washers to prevent galvanic corrosion between aluminum and steel.
Validate park lamp continuity by probing connector C502 (driver’s side B-pillar) at pin B14. An open circuit suggests a broken wire strand inside the door jamb harness–cut back 15 mm of insulation, expose fresh copper, and solder a new 14-gauge jumper to terminal G412.
Map the dome light circuit using a tone generator attached to the violet/white wire at bulb socket L17. Silence at fuse F1 (15A, interior lights) indicates a severed conductor at harness pinch point H3 near the steering column tilt lever–redirect the wires through conduit sleeve P31 to avoid future stress fractures.