P21E8

Code

Generic P — Powertrain

Cylinder 7 Injector B Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 21 EN: 24 RU: 23

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Causes

Short to ground in the injector B wiring for cylinder 7
Open or high-resistance connection in the injector harness or connector
Failed injector (internal short or coil issue)
Poor or missing power supply or ground to the injector circuit
Faulty PCM/ECM driver output for injector B
Corrosion, water ingress, or physical damage to connector/wiring

Symptoms

Check Engine Light (MIL) illuminated with stored P21E8
Rough idle or engine misfire on cylinder 7
Reduced engine power, hesitation or stalling under load
Increased fuel consumption and possible black smoke if injector stuck open
Intermittent fault or CEL that may clear when wiring is moved (intermittent contact)

What to check

Retrieve freeze frame and live data with a scan tool; note misfire counts and fuel trim
Visual inspection of injector 7 B connector, wiring harness, and nearby components for damage
Check for corrosion, moisture or bent pins at the injector connector
Measure battery voltage at key-on and during cranking to confirm proper supply (11–14 V)
Backprobe injector connector to measure voltage and signal while cranking/idle
Measure injector coil resistance (static) and compare to specification

Signal parameters

Injector coil resistance: typically ~1–16 ohms (varies by vehicle). Compare to OEM spec.
Supply voltage (key on): ~11–14 V at injector harness power feed
Driver output: pulsed ground or pulsed voltage depending on architecture — expected to toggle between ~0 V and ~battery voltage during injection
Pulse width: depends on engine operating conditions — from ~1 ms (idle) to >10 ms under load
Switching frequency: varies with engine speed; use scope to verify clean square pulses without clipped amplitude

Diagnostic algorithm

Confirm the code and record freeze frame and live data (misfire counters, injector duty).
Visually inspect cylinder 7 injector B connector and wiring for damage, corrosion, or disconnection.
With ignition ON (engine OFF), check for proper battery voltage at the injector power feed; if absent, check fuses/relays and related circuits.
Backprobe the injector B connector while cranking or running: verify driver signal present and that voltage swings to expected levels (0 V to battery voltage or vice versa).
Measure static coil resistance of the suspect injector out of circuit and compare to spec. A very low or near-zero reading indicates an internal short; infinite/open indicates open circuit.
If static resistance looks OK but signal is low, use a lab scope to check waveform at the injector driver for clipped pulses or abnormal duty cycle.
Perform a continuity/insulation test on the wiring between injector connector and PCM pin for shorts to ground or open circuits (pin-to-pin resistance and short to ground).
Swap the suspect injector with another same-cylinder or same-bank injector (if practical) and see if the fault/behavior follows the injector or stays with cylinder 7. If the fault follows the injector, replace the injector.
If fault remains on cylinder 7 after swap, inspect/repair wiring or connector and re-test. If wiring is good, suspect PCM driver failure and verify by bench testing or replacing PCM according to OEM procedures.
Clear codes and road-test to confirm repair. Re-scan to ensure code does not return and that engine runs normally.

Likely causes

Damaged insulation or chafed wire touching chassis ground on cylinder 7 injector B circuit
Loose, corroded, or pushed-out terminal at the injector connector reducing voltage
Injector coil partially shorted internally producing abnormally low circuit voltage
Blown or high-resistance fuse/relay in the injector power feed or shared supply
PCM output transistor partially failed causing low or collapsed drive voltage