Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!

P1406 1997 GMC W4

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4 years 3 months ago #35685 by HarryL
P1406 1997 GMC W4 was created by HarryL
I am having an issue with a 1997 GMC W4/NPR with a 5.7L V8 engine. P1406 code. I have been doing some work to it and during the past couple of days I have been taking it out for test drive and the code shows up. I can manually make the pintle open and close based on Paul's video, but when I try the bi-directional test with the scan tool nothing changes. My desired position stays at 0 and actual position also stays at 0, voltage at around .66.

When I manually energize the EGR valve on the other hand, the computer detects the voltage change and EGR position, but the desired position stays at 0.

I have tested the 5v ref, power, control, signal and ground (ground reads around .16v).

I am not sure what else to do at this point. Would this be the result of a bad computer and I need to replace it? I have also cleaned out the passages but no changes.

Not sure how to test the computer since the EGR won’t open or if I have a wiring or ground issue.

I appreciate the help.

Harry
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4 years 3 months ago - 4 years 3 months ago #35689 by Chad
Replied by Chad on topic P1406 1997 GMC W4
Circuit Description
The VCM constantly monitors the linear EGR valve pintle position sensor in order to ensure that the valve is responding properly to the commands from the VCM. The DTC P1406 is a type A DTC.

Conditions for Setting the DTC
The following condition will set the DTC:
♦ Ignition voltage greater than 9 volts
♦ The difference between the actual EGR position and the desired EGR position is greater than 10% for 10 seconds

Action Taken When DTC Sets
If a current DTC P1406 sets during 2 consecutive test cycles, the VCM turns ON the MIL.

Conditions for Clearing the MIL/DTC
The VCM turns OFF the MIL after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle) or the scan tool clearing feature has been used.

Diagnostic Aids
A poor connection or rubbed-through wire insulation may cause an intermittent. Check for the following conditions:

♦ Poor connection or damaged harness - Inspect VCM harness connectors for backed out terminals at EGR Control signal circuit, 5 Volt reference circuit, EGR sensor ground circuit, or Pintle position circuit for the following items:
♦ Improper mating
♦ Broken locks
♦ Improperly formed or damaged terminals
♦ Poor terminal to wire connection
♦ Damaged harness

Intermittent test - If connections and harness check OK, monitor a digital voltmeter connected between affected terminals and ground while moving related connectors and wiring harness. If the failure is induced, the voltage reading will change.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. Checks for an EGR valve sticking partially open or an incorrect pintle position sensor feedback signal.
3. This step determines if this DTC was set during an intermittent condition. If the fault that set this DTC is not present, check for other stored DTCs.
5. Checks the EGR valve driver in the VCM and the EGR Control circuit.
6. This checks for EGR Valve Ignition Feed at the EGR valve.
38. Clearing the DTC Information is a very important step in this diagnostic. This allows the EGR Valve to relearn a new minimum pintle position.

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"Knowledge is a weapon. Arm yourself, well, before going to do battle."
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Last edit: 4 years 3 months ago by Chad.
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4 years 1 month ago #37345 by jreardon
Replied by jreardon on topic P1406 1997 GMC W4
I'm sorry HarryL I just now saw your PM lol. Your ground reading of .16V is too high I think. ScannerDanner recommends less than .1V for sensor grounds. The high ground voltage would skew the position signal, thus setting the code. And ScannerDanner always says that some trouble codes will disable outputs from working. I would run a new ground wire from the battery to test this theory, clear the codes and see if they come back.
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