Purpose
This procedure verifies that the Injector Driver Module (IDM) on a 7.3L Power Stroke is
producing the correct injector firing voltage. Proper IDM voltage is critical for injector operation.
A failed IDM or low supply voltage can cause:
• Hard start
• No start
• Rough idle
• Misfires
• Contribution faults
• Dead injector banks
The IDM should produce approximately 110V DC during operation on most model years.
Anything below approximately 48V can prevent proper injector firing.
Required Tools
• Digital multimeter capable of reading DC voltage
• Backprobe pins or piercing probes
• Wiring diagram (recommended)
• Fully charged batteries
• Safety glasses
Safety Precautions
• The IDM produces high voltage.
• Do not probe injector outputs directly while cranking unless using proper insulated
equipment.
• Keep hands clear of moving engine components.
• Ensure batteries are fully charged before testing.
IDM Location
On most 1994.5–2003 7.3L Power Stroke trucks, the IDM is located:
• Driver side fender well
• Behind the air filter housing
• Mounted near the firewall
Preliminary Checks
Before testing IDM output voltage:
1. Verify both batteries are fully charged.
2. Inspect IDM connector for:
o Corrosion
o Moisture intrusion
o Burned pins
o Loose terminals
3. Check all engine and battery grounds.
4. Verify IDM fuse integrity.
5. Confirm ICP pressure and RPM signal are present during crank.
Step 1 – Verify IDM Power Supply
Key ON Engine OFF
Disconnect the IDM connector and inspect for damage.
Using a multimeter:
Check Battery Power
Probe the IDM power supply pins.
Expected reading:
• Battery voltage (typically 12–12.6V)
Check Grounds
Measure resistance from IDM ground pins to battery negative.
Expected reading:
• Less than 0.5 ohms
If power or ground is missing:
• Inspect fuses
• Check IDM relay
• Repair wiring before continuing
Step 2 – Verify IDM Output Voltage
Reconnect the IDM connector.
Backprobe the IDM voltage output monitoring circuit.
During Cranking
Have an assistant crank the engine while observing voltage.
Expected:
• Minimum 48 volts
• Typical healthy output:
o 90–115 volts
If voltage is:
Voltage Reading Possible Cause
90–115V Normal
48–90V Weak IDM or low supply voltage
Below 48V Failed IDM likely
0V No IDM operation or no PCM trigger
Step 3 – Check for IDM Enable Signal
If no IDM voltage is present:
Verify the PCM is commanding injector operation.
Check:
• RPM signal while cranking
• Cam Position Sensor operation
• PCM power and grounds
Without a valid RPM signal, the IDM will not fire injectors.
Common Failure Symptoms
Symptom Possible IDM Issue
Starts cold, dies hot IDM internal heat failure
One injector bank dead Failed IDM driver circuit
No injector buzz test IDM not powering injectors
Rough idle with contribution codes Weak IDM output voltage
No start with good fuel pressure IDM not firing injectors
Common IDM Related Trouble Codes
Possible codes include:
• P1293 – High Side Open Bank 1
• P1294 – High Side Open Bank 2
• P1316 – IDM Codes Detected
• Injector circuit contribution faults
Additional Notes
Low Battery Voltage Matters
The IDM is extremely sensitive to supply voltage.
Weak batteries or poor cables may cause:
• Low IDM output voltage
• Extended crank
• False injector faults
Always load-test batteries before condemning the IDM.
Recommended Next Checks if Voltage Is Low
If IDM voltage is below specification:
1. Verify battery voltage remains above 10.5V during crank
2. Inspect IDM harness for corrosion
3. Check under-valve-cover harness connectors
4. Verify PCM connection
5. Substitute with known-good IDM if available
This information has been provided by Diesel Care and Performance Service Department. All diagnostic and repair information is provided for informational purposes only and should be performed by qualified technicians using proper safety procedures. Diesel Care and Performance Inc. assumes no liability for injury, vehicle damage, diagnostic errors, or repairs performed using this information.