No-Crank With One Click - Power Is Good, Control Is Good, Then What?
A 2011 V6 pickup will not crank. The customer hears one click from the engine compartment when the key is turned to START. The battery measures 12.65 V at rest, headlamps are bright, and the terminals are clean and tight. With the key held in START, voltage at the starter B+ stud is 11.9 V and voltage at the starter S terminal is 0.0 V. You remove the underhood starter relay. With the key held in START you measure 12.5 V at relay cavity 86 and 0.2 V at cavity 85. You install a known-good relay; with the key held, the relay clicks, battery voltage appears at cavity 87, but the S terminal at the starter stays at 0.0 V. The cluster shows Park and the scan tool agrees.
1. Where is the open circuit, and what test confirms it?
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The open is between relay cavity 87 and the starter solenoid S stud.
Reasoning chain:
- 12.5 V at 86 and 0.2 V at 85 means the ignition feed and the PCM's ground-side driver are both present - control side is good.
- The relay clicks, and voltage appears at 87, so the relay and its contacts are good.
- Yet S stays at 0.0 V, so the wire, fusible link, splice, or connector between 87 and the solenoid is open.
Confirmation: disconnect the solenoid S lead, then measure resistance from cavity 87 to the S wire end - a reading above a fraction of an ohm means an open/high resistance. Better: jumper the circuit through a headlamp bulb and read voltage drop along the run, flexing the harness at the cowl and engine-mount bends where these harnesses fatigue. Repair, then re-check cranking voltage at S.
2. What would you conclude if voltage at cavity 87 had stayed at 0 V while the key was held and the relay clicked?
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Then the relay coil is energizing but the contact circuit has no feed or the relay is not actually transferring.
Check in this order:
- Cavity 30 feed - is battery voltage present at the relay socket with the relay out? A blown fuse or fusible link in the feed is the usual answer.
- Load the coil circuit. Your voltmeter draws almost no current; a corroded terminal can show 12.5 V and still not pass enough current to pull the relay in. Put an incandescent test lamp across 86 and 85. Bright lamp = driver can sink current. Dim or no lamp = high resistance in the coil feed or a failing PCM driver.
- Swap the relay with a known-good one of identical pinout and re-test before condemning the module.
- Confirm the PCM is actually being commanded to crank - check the range/transmission PID and immobilizer status, since a theft-deterrent no-start can inhibit the ground side.
3. Is 11.9 V at the starter B+ stud during crank acceptable? What would you check if it dropped to 9.5 V with the engine not turning?
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11.9 V is normal. A drop of roughly 0.7 V from a 12.65 V resting battery with the solenoid pulling in is expected.
If it fell to 9.5 V with no cranking:
- No crank means no starter inrush, so a drop that large points to either a very high resistance in the B+ or ground path, or a solenoid/starter that is drawing heavily without turning the motor.
- Do a cranking voltage drop on both sides: battery positive post to starter B+ stud (total B+ path generally under about 0.5 V), and engine block to battery negative post (generally under about 0.2 V).
- Load-test the battery separately - a battery that reads 12.6 V at rest can collapse under a 200+ A load.
- Inspect the engine-to-body ground strap and the block ground bolt, which are common corrosion points on this body style.