If your G37 powers on but won’t crank, check the battery, brake switch, steering-lock unit, IPDM relays, and starter circuit first.
Dash lights up. Radio works. The start button glows. Yet the engine won’t crank. This guide walks you through the fastest checks and the proven fixes owners and techs use on this platform. You’ll find a clear flow, two compact tables, and links to factory documentation so you can move from guesswork to a clean diagnosis.
Quick Triage: What To Check In The First 10 Minutes
Before diving into wiring, rule out the basics that commonly stall a start request on a push-button Nissan/Infiniti setup. These take minutes and often reveal the culprit.
- Press the brake firmly and hold it while pressing START. Watch for “ACC” or “ON” only. If it won’t enter “START,” suspect the brake pedal switch.
- Try a second fob. If the message says “No Key,” touch the fob to the button and retry. A weak fob battery or a dead cabin antenna can block authorization.
- Cycle the shifter to Park/Neutral. On manuals, press the clutch fully. A misread range/clutch switch blocks cranking.
- Listen for a single click under the dash/column. A failed steering-lock module can stop authorization to crank.
- Measure battery voltage at rest. You want near 12.6 V. Anything near 12.2 V or lower can light the dash yet starve the start request.
Early Diagnostic Table: Likely Causes, Tells, And First Moves
| Likely Cause | What You’ll Notice | First Action |
|---|---|---|
| Weak main battery | Bright dash, dim during START; relays click; no crank | Load-test or jump with a known good source; retest |
| Brake pedal switch misread | Stays in ACC/ON; prompt says “Press Brake” | Check brake lights; wiggle connector; test switch outputs |
| Steering-lock unit fault (ESCL) | “Key” lamp or lock icon; faint column click; no crank | Try lock/unlock cycle; check for ESCL campaign history |
| IPDM E/R relay logic fault | No crank despite valid START request; no starter feed | Scan for IPDM faults; verify relay commands and power |
| Starter motor or cable issue | Single loud click or dead silence at the bellhousing | Check “S” terminal during START; verify ground path |
| Fob battery or antenna issue | “No Key” message; works when fob touches the button | Replace fob coin cell; test interior antennas |
How The Start Request Travels On A G37
Knowing the path helps you test in order. On this platform the push-button, Body Control Module (BCM), and the engine-bay Intelligent Power Distribution Module (IPDM E/R) coordinate the crank request. When brake/clutch and immobilizer inputs look valid, the BCM tells the IPDM to energize the starter control, which feeds the starter solenoid. Infiniti’s service documentation shows that flow clearly, including the BCM and IPDM roles.
For wiring and control logic, see the factory Starting System section and the 2012 system diagrams hosted by charm.li. These sources outline the BCM→IPDM→starter path and the conditions needed for a valid crank.
Step-By-Step Checks With Tools You Already Have
1) Battery And Grounds
Dash lights can fool you. A battery with surface charge may power accessories but sag during a crank request. Check at the posts and again at the jump point. If a jump pack wakes the starter, service the battery and clean both ground straps.
2) Brake Pedal Or Clutch Switch
If the cluster keeps asking you to press the brake, the start request never armed. Press the pedal and check if the brake lights glow. Two switches live on the pedal assembly on many trims: one for lamps and one for the BCM/Intelligent Key path. A failed contact leaves the car stuck in ACC or ON with no crank. Nissan/Infiniti training notes flag a bad brake switch as a common no-start cause on I-Key vehicles.
3) Intelligent Key Recognition
Try both fobs. Replace the coin cell. If messages persist, touch the fob to the start button and retry; that uses a fallback antenna. If that works, chase the in-cabin antenna or the fob battery. Owner manuals describe this touch-to-start method and can help confirm the procedure.
4) Steering-Lock Module (ESCL) Symptoms
A stuck steering-lock can block engine cranking even when the dash powers up. You may hear a faint click in the column and see a warning lamp. Nissan issued service campaigns on related systems for sibling models (370Z/GT-R), noting a lock unit that may malfunction after parking and prevent starting. While chassis differ, the pattern matches what many G-chassis owners report. If you suspect this, ask a retailer to check VIN history for any steering-lock service actions.
5) IPDM E/R And Starter Command
When pedals and immobilizer inputs check out, the BCM asks the IPDM to pull in the starter control. If the starter “S” terminal never gets voltage during START, look at the IPDM command and grounds. Factory literature lists the IPDM’s internal relays for the start circuit and shows how the BCM energizes them. A scan tool that can talk to IPDM and BCM makes this faster, but you can still probe the “S” wire for live voltage during a helper’s START press.
6) Starter Motor And Cabling
A dead solenoid gives silence. A dragging starter gives a single heavy click. Verify the main cable for corrosion at the lug on the starter and the engine ground strap near the bellhousing. If the “S” terminal shows good voltage during START and the motor doesn’t spin, the starter needs work.
Close Variant Topic: G37 Power On, No Crank — Roadside Wins
Stranded in a lot? Try these quick moves that often work on this platform:
- Hard press on the brake while holding START for a few seconds; then release and try again.
- Touch the fob to the button and hold START. Swap to the spare fob.
- Shift to Neutral and retry START. Then back to Park and retry.
- Cycle lock/unlock with the fob, wait ten seconds, and retry START.
- Disconnect the negative cable for three minutes to reset modules; reconnect and retry.
Deeper Dives: What Each Suspect Looks Like Under Test
Brake Pedal Switch — Pin-By-Pin
Many trims use two switches: a two-wire lamp switch and a multi-wire signal switch to the BCM. On scan data, you’ll see two status bits change when the pedal moves. No change on the signal circuit means the BCM never sees a valid “brake pressed,” so it won’t allow crank. Infiniti service guides show voltage checks and thresholds for the switch harness.
Steering-Lock Unit (ESCL) — Tells And Remedies
Random no-start with power, intermittent column clicks, and no crank often trace back to the lock module. Some models had campaigns to replace the lock with a non-locking box to remove the failure mode. If your retailer confirms similar coverage in history for related cars, that context can guide your plan. A physical test involves listening at the column during START and confirming the lock pin retracts. Campaign documents state the lock can malfunction after the vehicle has been parked, then block the next start attempt.
IPDM E/R — Logic Versus Power
The engine-bay IPDM contains the starter control path. The BCM sends a request; the IPDM closes the control relay; the “S” circuit feeds the starter solenoid. If you have live request data but no solenoid feed, chase the IPDM ground, fuse feeds, and the harness to the starter. Factory starting-system PDFs illustrate the relay map and signal flow.
Fob Recognition — When Touch-Start Works
If the car starts only when the fob touches the button, the cabin antenna may be weak. Replace the coin cell and retest. If range returns, you found it. If not, scan the Intelligent Key system for related codes and test the antenna circuits.
Where A Scan Tool Speeds Things Up
A scanner that can see BCM and IPDM data trims hours off the chase. Look for:
- Brake switch status bits: both should flip when you press the pedal.
- Immobilizer authorization: “OK” before cranking.
- Starter request: BCM command goes from OFF to ON during START.
- IPDM starter relay command: follows the BCM request.
- DTCs: any B-codes for steering lock, Intelligent Key antennas, or range/clutch switches.
Parts, Tests, And Typical Outcomes
The table below helps you match symptoms to likely fixes after basic checks.
| Symptom | Probable Part/Area | What Usually Fixes It |
|---|---|---|
| ACC/ON only, no crank prompt | Brake pedal signal switch | Adjust/replace switch; repair connector |
| Random no-start with faint column click | Steering-lock module (ESCL) | Replace ESCL or upgraded box; check campaign history |
| Dash bright, no “S” terminal voltage | IPDM starter control or wiring | Repair IPDM feed/ground; harness to starter |
| Single loud click at bellhousing | Starter solenoid/motor | Replace starter; clean main cable and ground |
| “No Key” message clears when touching button | Fob battery or cabin antenna | New coin cell; test/replace antenna module |
| Starts with jump, then quits again | Main battery weak or loose ground | Battery and ground service; charging test |
Where Official Docs Help
When you want exact wiring, connector faces, and pin numbers, lean on factory literature. The G-platform starting-system PDF shows the BCM and IPDM roles and relay logic. For steering-lock behavior that can block cranking after parking, Nissan’s service-campaign bulletins for related models provide useful context and dealer language. Linking straight to the correct pages beats guesswork:
- Starting System — Infiniti factory manual (STR) for flow, relays, and tests.
- Electronic Steering Column Lock campaign bulletin that explains a lock that can prevent engine start after parking on sibling platforms.
DIY Safety And When To Hand It Off
Disconnect the negative cable before unplugging control modules. Keep metal tools clear of the battery’s positive post and the starter stud. If you need to bridge the starter to test the motor, use eye protection and mind the car’s gear position and parking brake. If the “S” terminal sees power and the motor stays silent, or if you have IPDM control faults, plan for professional diagnostics.
Repair Paths That Stick
Battery And Grounds
Install a fresh battery if load-testing shows sag. Clean and tighten the ground strap from block to chassis and the main cable at the starter. Many intermittent no-crank complaints fade after this service.
Brake/Clutch Switch Replacement
Switches are inexpensive and easy to swap. Adjust the plunger so the status bit shows pressed only when your foot is down. Confirm with a scan or lamp test.
Steering-Lock Unit Replacement
If the column module proves faulty, some service paths replace it with an updated box designed to remove the lock function that can stick. Campaign files describe this approach for related models, preventing a repeat stall. Dealer access to VIN history will tell you what’s already been done and what parts apply now.
IPDM And Starter Circuit Repairs
Corroded grounds, weak relay feeds, or a damaged “S” wire will block the solenoid. Verify feeds and grounds at the IPDM. Confirm continuity to the starter. If a starter relay driver inside the IPDM fails, replacement of the unit is the clean fix on many builds since the relay is internal. The factory STR section documents the control path end-to-end.
Frequently Missed Clues
- Brake lights do work, yet the start request still fails. That often points to the second switch on the pedal that feeds the BCM, not the lamp circuit.
- A bright dash can hide a weak battery. Voltage drop under load tells the real story.
- Touch-to-start succeeds while normal proximity fails. That points to an in-cabin antenna or a fob cell, not the immobilizer core.
- A faint click near the column followed by silence. That is classic for a steering-lock hang-up.
Bottom Line
Most “powers on, no crank” cases trace back to one of five spots: the main battery, the brake/clutch switch, the steering-lock unit, the IPDM’s start control, or the starter itself. Work the quick triage list, verify the start request path, and confirm voltage at the “S” terminal. With the factory STR diagrams and the steering-lock campaign context in hand, you can pin the fault without parts-cannon guessing.