Code
P1600
GEO
P — Powertrain
PCM Battery Circuit Fault
Views:
UK: 41
EN: 60
RU: 47
AI status
Completed
Completed
100%
Causes
- Low or dead battery
- Corroded, loose, or damaged battery terminals/cables
- Poor chassis or engine block ground straps
- Blown or corroded PCM/ignition power fuse or fusible link
- Damaged or disconnected PCM power/ground wiring or connector
- Faulty ignition switch or accessory power distribution
Symptoms
- MIL (Check Engine Light) illuminated
- No crank or no start (if battery/starting circuit affected)
- Intermittent stalling or loss of engine control
- Loss of communication with PCM using a scan tool
- Erratic instrument cluster or accessory operation
- Memory functions (radio presets, clock) reset or lost
What to check
- Measure battery resting voltage (key off) and voltage while cranking with a digital voltmeter
- Inspect and clean battery terminals, cable ends, and grounding straps
- Check all PCM-related fuses and fusible links for continuity and correct rating
- Visually inspect PCM connector and wiring harness for corrosion, damage, or loose pins
- Use a scan tool to attempt communication with the PCM and note any related codes
- Backprobe PCM power (B+) and ignition-switched supply pins for correct voltages (key on/crank)
Signal parameters
- Battery voltage (key off) — expected ~12.4–12.7 V (charged)
- Battery voltage (key on, engine off) — ~12.4–13.0 V
- Cranking voltage — should not drop below ~9.5–10.5 V (varies by vehicle)
- PCM B+ supply voltage (key on and during crank) — should match battery plus any small drops
- Ignition-switched voltage to PCM (key on)
- Ground circuit resistance to chassis/engine (low milliohms preferred)
Diagnostic algorithm
- Record freeze frame and all stored codes with a scan tool; note intermittent flags and time of occurrence.
- Measure and record battery voltage at rest and while cranking. If battery voltage is low, charge or load-test the battery and retest.
- Visually inspect and clean battery terminals, cable ends, and engine/chassis grounds. Tighten connections to proper torque and recheck voltages.
- Check all fuses/fusible links in the battery/IGN/PCM power distribution (include underhood power distribution box). Replace any blown or corroded items.
- With key ON, backprobe the PCM power (B+) and ignition-switched supply pins. Confirm stable battery voltage present. If missing, trace wiring back to fuse/relay/ignition switch to find open or high-resistance section.
- Inspect PCM connector for corrosion, bent pins, or water intrusion. Repair/replace damaged terminals or harness sections as needed.
- Perform a wiggle/stress test on harness while monitoring supply voltage and scan tool connectivity to identify intermittent open/short.
- Check charging system (alternator) output and voltage regulator if system voltage low or fluctuating.
- If parasitic drain suspected, perform current draw test and isolate circuit with fuses removed to find source.
- After repairs, clear codes and test-drive. Re-scan to verify code does not return. If wiring, fuses, battery and charging system check good and fault persists, consider PCM replacement only after confirming with factory diagnostics and reprogramming procedures.
Likely causes
- Weak or discharged battery failing to provide stable voltage
- Corroded/loose battery negative/positive connections
- Blown PCM power fuse or failed fusible link
- High resistance in PCM power or ground circuit due to corrosion or damaged wiring
- Intermittent connector contact at PCM causing voltage loss
Fault status
Status
PCM reported battery/power circuit fault — verify battery, fuses, power/ground wiring, and PCM power connections.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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