Battery Voltage Below Cranking Threshold Detected
What does PERKINS-168-4 mean?
The PERKINS-168-4 (Perkins EST) diesel fault code means: Battery Voltage Below Cranking Threshold Detected. This is a moderate severity code.
Common Symptoms
- Panel displays fault code 168-4 and a battery or voltage warning lamp lights up
- Generator fails its weekly or monthly automatic exercise cycle without cranking
- Generator cranks slowly or sluggishly before shutting down on a cold morning
- Yellow alarm LED on the PowerWizard controller is solid or flashing
- Remote monitoring via OnCue or Mobile Link shows a battery fault alert
- Generator starts manually but struggles to reach idle RPM before cutting out
- ATS does not transfer the load because the genset never completes the start sequence
Probable Causes (Ranked by Likelihood)
- Weak or sulfated battery that can no longer hold a charge above the minimum cranking voltage (typically 10.5 V DC on a 12 V system or 21 V DC on a 24 V system) Very Likely
- Faulty or undersized battery charger (float charger) that is not maintaining the battery between exercise cycles Very Likely
- Corroded, loose, or high-resistance battery cable connections at the battery terminals, starter motor, or engine block ground Likely
- Battery charger circuit breaker or fuse has tripped or blown, cutting off the trickle charge to the battery Likely
- Parasitic DC draw from a panel accessory, heater element, or wiring fault slowly draining the battery between starts Possible
- Failed or weak starter motor drawing excessive current and collapsing battery voltage below the controller threshold during cranking Possible
- Battery voltage sense wire or pin in the controller harness is damaged, corroded, or has a poor connection, giving a false low reading Less Likely
Step-by-Step Diagnostic Procedure
Step 1 -- Safety first. Set the panel switch to OFF before touching any wiring. Make sure the automatic transfer switch (ATS) cannot command a remote start while you are working.
Step 2 -- Measure resting battery voltage. With the engine off and the panel in OFF, set your multimeter to DC volts and place the red probe on the battery positive terminal, black probe on the negative. A healthy 12 V battery should read 12.6 V to 12.8 V. A 24 V battery bank should read 25.2 V to 25.6 V. Anything below 12.2 V (12 V system) or 24.4 V (24 V system) at rest confirms a weak or discharged battery.
Step 3 -- Check the battery charger output. Locate the small trickle or float charger wired into the panel. Measure DC voltage at its output terminals. It should read 13.2 V to 13.8 V on a 12 V system (27.0 V to 27.6 V on 24 V). No output or output below 12.8 V means the charger is not doing its job. Check the charger fuse or breaker first -- these trip more often than people expect.
Step 4 -- Inspect cable connections. Look at both battery terminals, the ground cable where it bolts to the engine block, and the positive cable at the starter motor solenoid. Wiggle each connection. Any movement, visible green or white corrosion, or heat discoloration means resistance is building up there. Clean terminals with a wire brush and tighten all fasteners. Battery terminal corrosion alone can drop voltage by 1 to 2 V under cranking load.
Step 5 -- Load-test the battery. If you have a battery load tester, apply a load equal to half the battery's cold-cranking amp (CCA) rating for 15 seconds and watch the voltage. It must not drop below 9.6 V (12 V system) or 19.2 V (24 V system). If voltage collapses under load, the battery cannot supply cranking current and must be replaced regardless of its resting voltage. Many auto parts stores will do this test free of charge.
Step 6 -- Check for parasitic draw. With everything off and the battery fully charged, clamp an amp meter in series with the negative battery cable. A healthy genset should draw no more than 50 to 100 mA at rest from block heaters and the controller keep-alive circuit. A draw above 200 mA suggests a short or a faulty accessory and requires further tracing.
Step 7 -- Inspect the voltage sense wiring. Follow the small-gauge wire from the battery positive terminal to the controller. Look for chafed insulation, a pushed-back pin at the controller connector, or a corroded ring terminal. A bad sense connection can cause the controller to report a false 168-4 even with a good battery. This step may require the wiring diagram for your specific FG Wilson or Perkins package. If you cannot locate the sense wire, this is the point to call a technician.
Step 8 -- Clear the fault and test. After correcting the most likely cause, switch the panel to AUTO and allow the battery charger to bring the battery to full charge for at least two hours. Then command a manual exercise run from the panel. Watch the battery voltage reading on the PowerWizard display during cranking. If voltage stays above 10.5 V (12 V) or 21 V (24 V) and the unit starts cleanly, the fault is resolved. If 168-4 returns immediately, the fault is likely internal to the controller or the starter circuit and requires Perkins EST diagnostics by a qualified technician.
Frequently Asked Questions
What does Perkins code 168-4 mean?
It means the controller measured the battery voltage and found it below the minimum level needed to reliably crank the engine. On a 12 V system the threshold is typically 10.5 V DC. On a 24 V system it is around 21 V DC. The controller logs the fault to protect the starter motor and prevent a failed-start event from being invisible to you or your monitoring system.
Can my generator still run with code 168-4 active?
It depends on when the fault was logged. If the battery dropped low during a failed exercise attempt but has since recovered, the unit may still start in an emergency. However, if the battery is genuinely weak, it may crank too slowly to fire the engine or may not crank at all. Treat this as a time-sensitive issue. Do not assume the unit will start when the power goes out.
How much does it cost to fix Perkins code 168-4?
If the fix is just cleaning corroded battery terminals, your cost is under $20 and about 30 minutes of your time. A new battery for a smaller FG Wilson unit (30 to 80 kVA) runs $100 to $200 in parts. Larger Perkins platforms using a 24 V dual-battery bank can cost $400 to $900 in batteries plus a pro service call of $150 to $300 for labor and inspection. Replacing a failed trickle charger is typically $80 to $200 for parts and can be done DIY.
Will the generator start the next time the power goes out?
Not guaranteed. A weak battery that triggered 168-4 during an exercise cycle is the same battery that will attempt to crank the engine during a real outage, often at night or in cold weather when voltage sags further. Do not clear the code and walk away. Fix the root cause -- usually a bad battery or charger -- before you rely on the unit for standby power again.