Power Stroke Glow Plug Problem - How to Fix It

Power Stroke Glow Plug Relay

The Power Stroke Diesel engine relies heavily on the glow plug system. This time of year, when temperatures get low, it can be especially critical that the glow plug system is working properly. 

Diesel engines are up to 30% more efficient than gasoline engines, they use high compression to ignite the fuel rather than spark plugs. High-pressure fuel injectors spray fuel directly into the combustion chambers when the pistons near top dead center. The heat of this compression, combined with residual heat in the piston and cylinder head from the previous power stroke, ignites the fuel.

Due to this design approach, a diesel engine can be hard to start when the engine is cold. Since there is no residual heat in a cold engine, some means of supplemental heat must be provided to make cold starting easier, especially when the outside temperature drops below freezing. Without this supplemental heat, a diesel engine may not start at all. It will just crank and blow white smoke (unburned fuel vapor) out of the tailpipe.

The following DTCs (Diagnostic Trouble Codes) are related to the Power Stroke Glow Plug System:

P1391 Glow plug circuit low input, bank #1 (right) Open/short/miswired circuit, faulty relay, glow plugs.

P1393 Glow plug circuit low input, bank #2 (left) Open/short/miswired circuit, faulty relay, glow plugs.

P1395 Glow plug monitor fault, bank #1 One or more glow plugs failed or circuit fault.

P1396 Glow plug monitor fault, bank #2 One or more glow plugs failed or circuit fault.

DTCs P1391 and P1395 Right Bank, P1393 and P1396 Left Bank and P1994 Center Monitoring Circuit.

Note: The glow plug system is monitored when the glow plugs are commanded on for more than 35 seconds and battery voltage is between 11.5-14 volts. DTC P1395 or P1396 will set on the bank that is reading less than 39 amps. Loose fitting pins in the circuit connectors causing high resistance or high-resistance glow plug(s) on that bank could be the cause. A shorted circuit or low-resistance glow plug(s) on the opposite bank could also be the cause. Each bank needs to draw more than 39 amps.

DTC P1391 or P1393 will set when the monitor indicates that all four glow plugs are not being powered on that bank. An open in the glow plug circuits, glow plug relay, glow plugs or monitoring circuit could be the possible causes.

Both DTCs P1391 and P1393 together will set when the monitor indicates that all eight glow plugs are not being powered. An open in all glow plug circuits, the glow plug relay, glow plugs, fusible links or all three monitoring circuits could be the possible causes.

Possible causes:

  • glow plug relay
  • glow plug shunt
  • open in glow plug circuit(s) or monitoring circuit(s)
  • glow plugs
  • PCM

7.3L Power Stroke Glow Plugs:

  • F4TZ-12A342-BA Motorcraft Part Number: ZD-11
    Application: 1994-2003 F-250 through F-550 (50 State)

7.3L Power Stroke Glow Plug Relay:

  • F7TZ-12B533-CA Motorcraft Part Number: DY-860
    Application: 1994-2003 F-250 through F-550 (50 State)
  • F81Z-12B533-AC Motorcraft Part Number: DY-861
    Application: 1997-2003 F-250 through F-550 (50 State)

Power Stroke Wiring Diagram

Measure voltage of Circuit 38 (BK/O) between glow plug relay and ground. If voltage is not greater than 10.5 volts, REPAIR open Circuit 38 (BK/O) or fusible links. CLEAR DTCs and RETEST. Else, if voltage is greater than 10.5 volts, perform KOEO (Key On Engine Off) On-Demand Self Test and retrieve Continuous DTCs. If DTC P0380 is present, DTC P0380 is set when the PCM detects a malfunction in the glow plug relay control circuit. Possible causes:

  • shorted to power
  • open/grounded circuit
  • open fuse (F-Series - Fuse 30, Econoline - Fuse 8)
  • worn or damaged glow plug relay

DTC P0380 Key on, engine off. Measure voltage at glow plug relay Point B, Circuit 16 (R/LG) for Econoline or 361 (R) for F-Series, and battery ground.

If voltage is not greater than 10.5 volts, repair open in ignition power Circuit 16 (R/LG). If fuse is blown, Check for short to ground. Clear DTCs and retest.

If voltage is greater than 10.5 volts, do a RELAY COIL RESISTANCE TEST, with the key off, by disconnecting the wire going to the glow plug relay, circuit 1086 (P/O) point A. Measure resistance through relay coil, between Point A and Point B. If the resistance is not between 1 ohm and 8 ohms, replace glow plug relay. Clear DTCs and retest.

If resistance is between 1and 8 ohms, check short to power by installing a breakout box; leave PCM and wire 1086 (P/O) disconnected. Key on, engine off. Measure voltage between PCM Test Pin 101 and battery ground. Key off. If voltage is greater than 10.5 volts, repair short to power in circuit 1086 (P/O). Clear DTCs and retest. If not,check short to ground by measuring the resistance between PCM test pin 101 and battery ground.

If resistance is not greater than 10,000 ohms, repair short to ground in circuit 1086 (P/O). Clear DTCs and retest.

If resistance is 10,000 ohm or greater, check circuit for open, by measuring resistance between PCM Test Pin 101 and Circuit 1086 (P/O) eyelet going to glow plug relay. If resistance is less than 5 ohms, replace PCM. Clear DTCs and retest. If resistance is 5 ohms or greater, repair open in circuit 1086 (P/O), clear DTCs and retest.

CHECK GLOW PLUG RELAY

Note: The glow plug ON time is dependent on oil temperature and altitude. The glow plugs come on between 1 to 120 seconds depending on oil temperature and do not come on at all if EOT(Engine Oil Temperature) is above 55°C (131° F) for F-Series or 30°C (86° F) for Econoline. Verify glow plug control ON time using PID GPCTM (Glow Plug Control Time). EOT temperature below 55°C (131°F) for F-Series or 30°C (86°F) for Econoline. With the key on, engine off, measure voltage between center terminal of glow plug shunt and battery ground. If voltage is not present for at least 30 seconds, replace glow plug relay. If voltage is present for a least 30 seconds, Check Glow Plug, with the key off, by disconnecting the connector on the valve cover gasket and measuring the resistance between each of the four glow plug circuits on adapter and engine ground (clean off a spot on the high-pressure oil reservoir to ensure a good ground).

If resistance is not less than 2 ohms, check under valve cover and verify that the connections to the glow plugs are OK. If OK, disconnect the suspect glow plug connector. Measure resistance between the glow plug and engine ground. If resistance less than 2 ohms, Replace valve cover gasket or UVC harness, clear DTCs and restest. If resistance is not less than 2 ohms, replace glow plug, clear DTCs and restest.

CHECK GLOW PLUG MONITORING CIRCUIT - DTCs P1391, P1395

Disconnect connectors on both right and left banks.
Install breakout box; leave PCM disconnected.
Measure resistance between all four glow plug circuits on the right bank and PCM Test Pin 9.
Are all readings within 2 ohms of each other? If not, repair open between valve cover connector and PCM connector. Verify glow plug shunt nuts are clean and tight. Clear DTCs and retest.

CHECK GLOW PLUG MONITORING CIRCUIT - DTCs P1393, P1396

Measure resistance between all four glow plug circuits on the left bank and PCM Test Pin 34. Are all readings equal and less than 2 ohms?

COMPARE RIGHT BANK TO LEFT BANK Record all readings. The circuits must be within 2 ohms of each other. Measure resistance between all four glow plug circuits on left bank and PCM Test Pins 8, 9 and 34, then all four glow plug circuits on right bank and PCM Test Pins 8, 9 and 34. Are all readings within 2 ohms of each other? If not, repair open in the higher resistance circuit.

DTC P1397 - SYSTEM VOLTAGE OUT OF SELF-TEST RANGE DURING KOER GLOW PLUG MONITOR SELF TEST

Note: DTC P1397 will set if system voltage is above 14 volts or below 11.5 volts at any time during KOER (Key On Engine Running) Glow Plug Self Test. It may be necessary to raise rpm to maintain voltage. If unable to maintain system voltage, service as required according to service manual direction. Perform KOER Glow Plug Monitor Self Test. With a digital multimeter connected to the battery. Maintain system voltage until test is complete.

Testing the Power Stroke Glow Plug Relay for proper operation:

Glow Plug Resistance Check 7.3 Powerstroke: