P1600

Code

CADILLAC P — Powertrain

PCM Battery

Brand: CADILLAC

Type: P — Powertrain

Views: UK: 59 EN: 83 RU: 53

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Page language: EN

Causes

Low or weak vehicle battery (state of charge or internal resistance out of spec)
Poor or corroded battery terminals or cable connections
Open/blown main fuse or fusible link supplying PCM
Damaged or shorted battery feed or ground wiring to PCM
Faulty or loose PCM connector or pin(s)
Faulty charging system (alternator) causing low/high system voltage

Symptoms

Malfunction Indicator Lamp (MIL) illuminated
No communication with PCM or intermittent scan tool connection
No-start or hard-start conditions (cranks but will not run or runs poorly)
Random stalls or loss of engine power
Loss of memory items (radio presets, learned values) after shut off
Erratic gauges or electrical accessories

What to check

Scan vehicle and record freeze frame and any related codes; note intermittent/pending status
Measure battery open-circuit/resting voltage (engine off)
Measure battery voltage during cranking and while engine running
Visually inspect battery terminals, cable condition, and chassis/engine grounds
Inspect main fuses, fusible links and power distribution for damage or opens
Inspect PCM connector for corrosion, bent pins, water intrusion or damaged terminals

Signal parameters

Battery resting voltage (engine off): approx. 12.4–12.8 V (fully charged ~12.6 V)
Key ON, engine OFF (KOEO) system voltage: approximately battery voltage (12.0–14.6 V depending on state of charge)
Cranking voltage: typically should not drop below ~9.0–10.0 V for most modern vehicles; lower values indicate weak battery or high resistance
Charging voltage (engine running): 13.5–14.8 V
Acceptable voltage drop from battery positive to PCM power pin: typically
Acceptable ground path resistance PCM-ground to battery negative: typically

Diagnostic algorithm

Retrieve codes and freeze-frame. Note when P1600 sets (key on, cranking, driving, after jump start).
Verify battery condition: measure open-circuit voltage and perform a load/cranking test. Replace weak battery before further diagnostics.
Visually inspect and clean battery terminals, cable ends, and chassis/engine grounds. Tighten to spec.
Check main power fuses / fusible links in the power distribution center; replace any open devices and re-test.
With ignition ON, measure voltage at the PCM power supply pin(s). Compare to battery positive. Look for excessive drop or intermittent loss.
Perform voltage drop tests: battery positive to PCM power pin under load, and PCM ground pin to battery negative. High drop indicates wiring/connection issue.
Inspect PCM connector for corrosion, bent pins or water intrusion. Wiggle-test wiring while monitoring voltage and communication to reproduce intermittent faults.
Test charging system (alternator output and regulator) for correct voltage and ripple. Repair if out of spec.
Clear codes and attempt to re-create fault. If P1600 returns, correlate with measured voltage events or connector faults.
If wiring, grounds, battery and charging system check OK and fault persists, consider PCM replacement or bench testing as last step. Follow manufacturer service information for PCM replacement and programming.

Likely causes

Corroded/loose battery terminals or cable clamp causing intermittent supply
Low battery voltage or weak battery unable to maintain supply during cranking
Blown main power fuse/fusible link to PCM
High resistance ground strap or poor engine/chassis ground to PCM
Damaged power feed wiring or connector at PCM
Alternator not charging or producing over/under voltage

Fault status

⚠️ Status

PCM reports a battery/power supply fault: main supply voltage to the PCM is out of expected range, is intermittent, or the PCM detects an internal power circuit issue. Check battery, connections, fuses and wiring before replacing the PCM.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours

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