Code
P1668
FORD
P — Powertrain
PCM IDM Communications Error
Views:
UK: 20
EN: 45
RU: 24
AI status
Completed
Completed
100%
Causes
- Damaged or shorted wiring between PCM and IDM
- Corroded, loose or bent connector pins at PCM or IDM
- Failed Ignition Driver Module (IDM)
- Failed or intermittent PCM communication circuitry
- Poor or missing ground or battery supply to one of the modules
- Water intrusion or contamination in connectors
Symptoms
- MIL/Check Engine lamp illuminated
- No-start or intermittent no-spark condition (if IDM is required for ignition)
- Engine stalls or runs poorly under certain conditions
- Loss of module data or IDM not present in scan tool network
- Intermittent faults that may clear and return
What to check
- Read freeze frame and full DTC list with a capable scan tool; note related codes
- Verify battery voltage is within spec (engine off and cranking)
- Check for IDM presence on scan tool module list and attempt to communicate with IDM
- Visually inspect PCM and IDM connectors for corrosion, bent pins, moisture, or push-out pins
- Perform wiggle test of wiring while monitoring communication status with a scan tool
- Inspect and test main grounds and power feeds for PCM and IDM
Signal parameters
- Communication activity on the IDM/PCM line(s) — must show regular data/messages on scan tool or oscilloscope
- Battery voltage at both module power pins (nominal ~12V) and during cranking
- Ground resistance from module chassis pins to battery negative (low milliohms preferred)
- Wiring continuity and insulation resistance between PCM and IDM connectors
- No short to battery or ground on communication/signal wires
Diagnostic algorithm
- Connect OEM-capable scan tool, read and record all codes and freeze-frame. Note related communication or ignition codes.
- Verify battery voltage and charging system (low voltage can cause communication faults). Repair battery/charging issues first.
- Visually inspect PCM and IDM connectors and harness; repair damaged connectors, clean corrosion, and secure pins.
- Check power and ground circuits: verify fused power to IDM and a good chassis/engine ground at both modules.
- Using a meter or scope, check the communication line(s) for activity and proper voltage levels; compare to a known-good vehicle or factory values when available.
- Perform continuity and resistance checks between PCM and IDM signal pins with connectors disconnected. Repair any opens, shorts, or high resistance.
- If wiring and power/grounds are good, try re-flashing or verifying module software/part numbers per manufacturer service information.
- If communication still fails and wiring/power/grounds/software verified, substitute a known-good IDM if available for confirmation before replacing PCM.
- After repairs, clear codes and perform a road/functional test; re-check for reoccurrence and re-scan for related codes.
Likely causes
- Wiring/connector damage or corrosion between PCM and IDM
- Poor ground or low battery affecting communications
- Defective IDM
- Faulty PCM communication circuit or software issue
- Intermittent connection (pin pushed out, broken strand)
Fault status
Status
PCM detected loss or invalid communication with the Ignition Driver Module (IDM); communication messages absent, corrupted, or out of expected timing/voltage range.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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