PCM/IDM Communication Error
The P1668 code indicates a communication failure between the Powertrain Control Module (PCM) and the Injector Driver Module (IDM). This typically occurs in Ford Power Stroke diesel engines. The IDM controls the fuel injectors, and the PCM sends commands to the IDM. When communication is lost, the engine may run poorly or not start. Common causes include wiring issues, faulty IDM, or PCM problems.
1. Symptoms You Will Notice
- Engine cranks but does not start
- Rough idle or misfire
- Check Engine Light illuminated
- Loss of power or poor acceleration
2. Most Common Causes
- Output circuit check wiring shorted to battery voltage (B+)
- Loose or corroded connections in the output circuit check harness
- Controlled actuator or solenoid with abnormal internal resistance
- Internal failure of the powertrain control module (PCM)
- Excessive resistance in the actuator ground circuit
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes to narrow down the issue.
Step 2: Visually inspect the IDM and PCM connectors for corrosion, damage, or loose pins.
Step 3: Check the wiring harness for breaks, shorts, or chafing between the PCM and IDM.
Step 4: Test the IDM power and ground circuits with a multimeter.
Step 5: If wiring is intact, swap the IDM with a known good unit to test.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
No, it is not safe. The engine may stall or fail to start, leading to a breakdown. Have it diagnosed immediately.
How much does it cost to fix?▼
Diagnosis typically costs $50-$150. Repair costs vary: wiring repairs $100-$300, IDM replacement $200-$600, PCM replacement $500-$1000.
5. Commonly Affected Makes
This is a manufacturer-specific code. The exact manufacturer is not confirmed in our current database.