OBD-II Code

P1659

Severity

Not yet reviewed

Nobody on our side has assessed this code yet, so we are not going to guess at how serious it is.

Can you drive it

We cannot say

Treat it as unknown until a shop reads it with live data. If the check-engine light is FLASHING, stop driving as soon as it is safe to — that means an active misfire, whatever the code.

Indicative cost (USD)

$180–$2,400

From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.

How a shop works this

Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.

Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then follow the diagnostic notes further down this page, in the order they are written.
They are written in the order a shop works this code, cheapest checks first. Where they name a component, inspect its wiring and connector before replacing it.

If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.

Common symptoms

Check engine light

Read the full diagnostic procedureP1659 is a Ford-specific code meaning the PCM detected a fault in the Cooling Fan 4 control circuit — specifically the high-side driver (HSD) inside…+

P1659 is a Ford-specific code meaning the PCM detected a fault in the Cooling Fan 4 control circuit — specifically the high-side driver (HSD) inside the PCM or the FCM (fan control module) failing to source the commanded current to the fan relay or PWM-driven brushless fan. On SuperDuty Powerstroke trucks this is the auxiliary/secondary fan stage that ramps in under high IAT or trans-temp load.

Shop-floor ladder cheapest-first

Visual + connector check — pull the FCM/fan-relay harness connector on the LH front of the radiator support, look for green corrosion or melted pins ($0, 10 min, catches roughly 35% of P1659s on 2003+ 6.0L/6.4L trucks where road salt eats the connector).
Key-on engine-off, command the fan on with a bidirectional scan tool and watch fan current on live data — a healthy clutched/electric Ford fan pulls 5-10A at low speed and 18-25A at full command; under 3A means open circuit (broken HSD or harness break), above 30A means a shorted motor or seized bearing dragging the driver into thermal shutdown.
Back-probe the FCM control wire — should see 0V key-off, then a PWM duty cycle from the PCM rising from ~10% to ~95% as commanded temp climbs. No PWM = PCM driver dead. Steady 0V or steady 12V with no modulation = harness short. Expensive-misdiagnosis caveat: before condemning the PCM for an internal HSD failure on a 6.0L Powerstroke, pull the FICM and FCM connectors and check for the well-known 'pin-fretting' pattern — Ford's HSD diagnostic logic will set P1659 when the FCM itself has a stuck relay or shorted MOSFET, and shops have replaced $1,800 PCMs only to find a $180 fan control module was the actual fault.

Vehicle-specific patterns1999-2007 Ford F250/F350/F450 SuperDuty with the 7.3L and 6.0L Powerstroke uses a dual cooling stack (engine-driven clutched fan + electric pusher/au…+

1999-2007Ford F250/F350/F450 SuperDuty with the 7.3L and 6.0L Powerstroke uses a dual cooling stack (engine-driven clutched fan + electric pusher/auxiliary), and P1659 specifically targets the electric stage — failure modes are corroded FCM connector on the LH radiator support, water intrusion into the FCM itself, and PCM HSD failure after a jump-start with reversed polarity.
2008-2010F250/F350 6.4L Powerstroke shares the same FCM architecture but adds a viscous-clutch sensor circuit that throws P1659 alongside P1247/P1248 when the clutch hub bearing fails.
2008-2010Ford Excursion (final-year 6.0L diesel chassis) sees P1659 from the same FCM corrosion path as the SuperDuty.
2011-2019F250/F350 6.7L Powerstroke moved to a brushless PWM fan with integrated controller — P1659 on these trucks almost always means the fan-internal driver board has failed and the whole fan assembly is replaced as a unit (no serviceable controller).

Estimated repair$180 to $2,400.

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