P1686

Code

PONTIAC P — Powertrain

No SKIM Bus Message Received

Brand: PONTIAC

Type: P — Powertrain

Views: UK: 17 EN: 48 RU: 25

AI status

Completed

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Page language: EN

Causes

Faulty SKIM (immobilizer) module
Open/shorted or corroded wiring/connectors on the SKIM bus, power or ground circuits
Low or intermittent battery/ignition supply voltage
Faulty ignition switch or immobilizer antenna (around ignition lock)
Loss of Class 2 / serial communication (bus fault)
Aftermarket electronics or radio interfering with data bus

Symptoms

Security/immobilizer indicator illuminated or flashing
Engine cranks but will not start (fuel/ignition disabled)
No crank or intermittent crank depending on theft logic
No SKIM messages visible on scan tool or intermittent communication
Possible stored related communication or theft codes

What to check

Read all stored and pending codes from all modules (PCM, BCM, SKIM if accessible). Note freeze frame data.
Check battery voltage and state of charge with key on/engine off (>12.2 V recommended).
Verify SKIM module fuse(s) and main power/ignition feeds.
Inspect SKIM, BCM and PCM connectors and wiring for corrosion, damage, or loose pins.
Scan the vehicle network for SKIM/Class 2 messages and look for other network communication DTCs (U-codes).
Verify security indicator lamp behavior during key on and cranking (lamp patterns often used for diagnostics).

Signal parameters

SKIM module power: ~12 V with ignition on; should be stable (no large drops)
Ground: continuity to chassis ground should be low resistance (
SKIM bus (Class 2/serial) should show regular message activity on scan tool; lack of messages indicates a bus or module fault
Message frequency: periodic SKIM/immobilizer messages visible on an appropriate scan tool (interval varies by model; expected repeated messages while key present)
No excessive voltage spikes or noise on the bus wiring when monitored with scope

Diagnostic algorithm

Retrieve all DTCs and freeze-frame data from PCM, BCM and body modules. Note other communication codes (U-codes) that may point to bus issues.
Verify battery state of charge and measure battery voltage with key on and during cranking. Recharge or replace battery if low.
Inspect fuses related to SKIM/immobilizer and replace if blown. Check inline fusible links if present.
Visually inspect and gently wiggle SKIM, BCM and PCM connectors and harness routes for damage, corrosion or rodent chewing. Repair any damaged wiring.
Backprobe/check for 12 V power and good ground at the SKIM connector with ignition ON. Repair power/ground faults before proceeding.
Use a scan tool capable of viewing Class 2/serial bus traffic and confirm whether SKIM messages are present. If no messages, isolate whether the bus is dead or the SKIM module is not transmitting.
If bus traffic is missing only for SKIM, check continuity of the bus wiring between SKIM and BCM/PCM and test for short to power/ground.
Try an alternate, known-good programmed key to rule out unrecognized transponder. If a spare works, reprogram or replace the faulty key.
Check immobilizer antenna ring (around ignition lock) and its connector for damage. Replace if antenna fails to read key transponder.
If wiring, power and grounds are good but no SKIM messages, attempt SKIM module reprogram/relearn per factory procedures. Some replacements require dealer-level programming.
If reprogramming fails or module does not respond, replace SKIM module and reprogram/relearn all keys and modules as required. After repair, clear codes and verify system operation.
If problem persists, investigate BCM/PCM communication circuits and consider module replacement or reflashing per manufacturer guidance.

Likely causes

Bad or unpowered SKIM module (no 12V or bad ground)
Damaged or loose connector at SKIM, BCM or PCM
Open or short on Class 2/serial bus wiring
Weak battery causing intermittent module power
Antenna ring or ignition coil antenna failure (key transponder not read)

Fault status

⚠️ Status

No SKIM (immobilizer) bus messages received. The PCM/BCM did not detect expected communication from the Sentry Key module; immobilizer may prevent engine start.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours

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P1686 — No SKIM Bus Message Received