Code
P1607
OLDSMOBILE
P — Powertrain
Serial Communication Problem With Device 7
AI status
Completed
Completed
100%
Causes
- Open, shorted, or intermittent wiring on the vehicle serial/data bus to Device 7
- Poor or missing power or ground to Device 7
- Corroded or loose connector(s) at Device 7 or along the network
- Faulty Device 7 (internal module failure)
- Bus contention or another module pulling the data line(s) low or high
- Software/configuration mismatch or corrupted module memory
Symptoms
- MIL (Malfunction Indicator Lamp) may be illuminated
- Loss of functions controlled by Device 7 (varies by vehicle)
- Intermittent or permanent module warnings/messages on dash
- Erratic behavior of systems tied to that module
- Other communication-related DTCs present
What to check
- Retrieve all stored and pending codes from all modules with a capable scan tool
- Identify which physical module is 'Device 7' from the factory service manual or wiring diagram
- Visually inspect connectors and wiring for Device 7 for corrosion, damage, or loose pins
- Verify battery voltage and good chassis/body and engine ground(s)
- Check for aftermarket components that tap into the data bus or electrical system
- Perform continuity and short-to-power/ground tests on the data and power/ground wires
Signal parameters
- Data-bus idle and active waveform (use factory spec or oscilloscope) — expected clean serial pulses without excessive noise
- Supply voltage to Device 7: nominal battery voltage (approx. 11–14.5 V with engine running)
- Ground integrity: near 0 ohms between module ground and chassis ground
- Bus resistance/termination: compare to factory specification (look for unusual low resistance indicating a short)
- No sustained bus-dominant condition when system is at rest (no continuous low/high lock)
Diagnostic algorithm
- Use a scan tool to read all codes and note any communication-related U-codes or additional P-codes. Record freeze frame and occurrence data.
- Consult the vehicle service manual to determine which physical module is labeled as Device 7 and review its wiring diagram.
- Visually inspect connectors at Device 7 and adjacent modules on the same bus. Disconnect and carefully inspect pins for corrosion, bent pins, pushed-back terminals, or water ingress.
- With the ignition off, perform resistance/continuity checks on the power and ground wires for Device 7 back to their source. Repair any open circuits or high-resistance grounds before proceeding.
- Inspect the serial/data bus wiring for damage along the harness route (pinch points, chafe locations, aftermarket splices). Repair or isolate any damaged sections.
- With the battery connected, verify supply voltage at Device 7 power terminal and measure ground voltage drop while cranking to confirm solid grounds.
- Use a lab-quality oscilloscope or a capable serial-data tester to probe the data line(s) at Device 7 and at the central controller while exercising the bus. Look for clean digital waveforms, proper idle levels, and no constant dominant state or excessive noise.
- If a short or abnormal device is suspected, disconnect Device 7 (or other removable modules) from the bus and observe whether the code clears or communications restore; this isolates a faulty module.
- If Device 7 is faulty and all wiring and power/grounds are good, follow OEM procedures for module reprogramming or replacement. After repair, clear codes and perform a full system recheck and road test to confirm repair.
- If intermittent, further isolate by wiggle-testing harnesses and performing extended road tests with datalogging enabled to capture the fault.
Likely causes
- Damaged or chafed harness conductor to Device 7
- Poor/chipped connector pins at Device 7 or at the BCM/ECM
- Failed ground strap or missing battery feed to Device 7
- Failed Device 7 communications circuitry
- Short to voltage or ground on the serial data line caused by aftermarket equipment
Fault status
Status
Serial communication fault detected: Device 7 failed to respond or produced invalid data on the vehicle serial/data bus. Check wiring, power/ground, and module communication.
Repair difficulty: Medium
Diagnostic time: 1.0-3.5 hours
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