P0616
PowertrainStarter Relay Circuit Low
The ECU has spotted that the control signal it sends to the starter relay is reading lower voltage than it should. For you, that usually shows up as a car that won't crank, or one that starts fine some mornings and gives you nothing on others. It points at a problem in the low-voltage trigger circuit that tells the relay to fire, not the heavy cables that actually feed the starter motor.
ⓘ Information only. This page provides general educational information about fault code P0616. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0616 mean?
P0616 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Starter Relay Circuit Low.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • No crank when you turn the key or press the start button, often with the dash lighting up as normal
- • A single click from under the bonnet, or dead silence, when you try to start
- • Intermittent starting, fine one minute and refusing the next, which makes it a pain to pin down
- • Engine warning light on with the no-start, sometimes the only clue you get
- • Starter motor doing nothing at all even though the battery is fully charged and the lights are bright
Possible causes
Causes commonly associated with P0616, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Starter relay itself failing internally, the contacts or coil winding degrading so the circuit reads low. This is the cheapest and most common culprit
- 2. Corroded or loose terminals in the fuse box or relay socket, very common on older cars and anything that's lived near the coast
- 3. Damaged or chafed wiring between the PCM and the relay, often where the loom rubs against a bracket or edge
- 4. Poor earth on the relay control circuit, a tired earth strap or corroded chassis point can drag the voltage down
- 5. Loose or backed-out connector pins at the PCM or relay plug, easy to miss on a visual
- 6. Failed PCM output driver controlling the relay, rare and the last thing you'd suspect after everything else checks out
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Pull the relay and inspect it, the socket, and the surrounding fusebox for corrosion, melted plastic or green crust on the pins. A surprising number of these are solved right here before a meter comes out
- 2. Swap the suspected relay for an identical one from another circuit, fuel pump or horn relays are often the same part. If it cranks, you've found it
- 3. Back-probe the relay control terminal and check the voltage with the start commanded, you're looking for somewhere in the 5V to 12V range. A low or absent reading confirms the circuit fault
- 4. Check earth continuity from the relay back to the chassis, you want under 0.1 ohms. Anything higher and you've got a duff earth dragging the signal down
- 5. Wiggle-test and inspect the loom between the PCM and relay for chafing, breaks or corroded connectors, paying attention to anywhere it crosses a metal edge
- 6. If the relay, earth and wiring all check out, the PCM output driver is the remaining suspect, and that's where you book it in rather than guessing
Common questions about P0616
What happens if I just leave it? +
Most likely you'll get stranded. P0616 commonly means the car won't crank at all, so leaving it isn't really a choice once it's stopped starting. If yours is still firing up intermittently, you're on borrowed time, and it tends to fail when it's cold, wet, or you're in a hurry. There's no engine damage risk from the code itself, but the inconvenience of a no-start in a car park is the real cost here.
How quickly do I need to sort this? +
Treat it as soon as you can, mainly because the symptom is a car that strands you. There's no rush in terms of mechanical harm, the engine isn't being damaged, but an intermittent no-start only ever gets worse. If you've had even one failed crank, get the relay and connections checked before you rely on the car for anything important.
Is it the relay itself or the wiring causing it? +
More often it's the relay or a corroded socket than a wiring fault, simply because relays are mechanical and wear out, and fusebox terminals corrode over the years. That's why swapping the relay is the first thing worth trying, it's cheap and quick. If a fresh relay doesn't clear it, then you're looking at the wiring, earth or connectors, and a PCM driver fault is the rare last resort once everything upstream tests good.
How long does the repair usually take? +
A straightforward relay swap is a five-minute job once you've found the right one, and a cheap part to boot, often well under £20. If it turns into chasing a wiring or earth fault, budget an hour or two of diagnostic time at a garage, which is where most of the bill goes. PCM-level repairs are a different ballgame and far less common, so don't assume the worst until the simple stuff is ruled out.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →